Our old printer finally passed away, so HomePi no longer provides AirPrint services, but here's the original raspbian recipe ... Last used on Stretch (cups 2.2.1) but  it should be close, CUPS is pretty solid and common.  Install/setup takes ~30 Mins.  Here's the original guide, it may be updated for Buster and beyond.
 

• Install avahi - required for network discovery
  sudo apt-get install avahi-discover 

• Installs CUPS and friends
  sudo apt-get install cups cups-pdf python-cups

• Mod user (e.g. user pi) to be CUPS admin, it will be used to login to web interface
  sudo usermod -aG lpadmin pi 

• Make sure CUPS and friends are running after the install
  ps -A | grep cups
  ps -A | grep avahi

CUPS Config, phase 1:  cupsd.conf
 

• Edit /etc/cups/cupsd.conf to permit remote browser access via port 631.   Double check Lynsay's guide, there were a number of edits here ... in case I miss one

  1. Comment out Localhost restriction & add line to permit access via port 631
     
     #Listen localhost:631
     Port 631

  2. Permit local network access to cups paths via local network - add "Allow @Local" line right after "Order allow,deny" in following sections for http(s) access to server, admin, config and log pages.  
     
     <Location />
       Order allow,deny
       Allow @Local
     </Location>
     <Location /admin>
       Order allow,deny
       Allow @Local
     </Location>
     <Location /admin/conf>
       AuthType Default
       Require user @SYSTEM
       Order allow,deny
       Allow @Local
     </Location>
     <Location /admin/log>
       AuthType Default
       Require user @SYSTEM
       Order allow,deny
       Allow @Local
     </Location>

  3. Remember to bounce CUPS after config updates
     
     sudo /etc/init.d/cups restart 

CUPS Config, phase 2 - via CUPS web interface @ http://<your PI IP address>:631 (https in latest cups)

• Log in to CUPS administration using pi system user & password 

• Administration page: check "Share Printers" and "Allow Remote Admin"

• Administration/Add Printer - "Discovered Network Printers" found our Dell M5200 w/ a couple of tweaks:

  • Set "Printer Description" to match your printer, it is presented in iPhone/Pad's 'Select Printer" dialog

  • I uses Openprinting.org ppd file to set up our printer - https://www.openprinting.org/printers

  • Remember to check the "Share this Printer" box
    
    

HowTo Use AirPrint to print from your iPhone, iPad, or iPod touch by Apple Support

HomeBridge is still not part of DietPi software library ... manual install required, but it's a LOT easier than it used to be!

This will still take some time, count on an hour with minimal plugin playtime! 

Homepage/info @ homebridge.io, github.com/homebridge/homebridge & Raspberry Pi specifics @ .../wiki/Install-Homebridge-on-Raspbian

• One important preliminary:  Check for plugins for your smart devices before you go through all this install stuff - just to make sure you'll be able to control your device.  Go to https://www.npmjs.com and search for  "homebridge-<your dev>".  For example "homebridge-wemo"  or "homebridge-" to browse the library.

• Also note - no need for sudo if you are logged in as root on DietPi

• Install Steps are dissected from *new* HomeBridge on Raspian Lite instructions

  • Install Node.js
    
    # setup repo
    curl -sL https://deb.nodesource.com/setup_12.x | sudo bash -
    # install Node.js
    sudo apt-get install -y nodejs gcc g++ make python
    # test node is working
    node -v
    # upgrade npm (version 6.13.4 has issues with git dependencies)
    sudo npm install -g npm

  • Install Homebridge and Homebridge Config UI X
    
    sudo npm install -g --unsafe-perm homebridge homebridge-config-ui-x
    # To setup Homebridge as a service that will start on boot use hb-service command.
    sudo hb-service install --user homebridge

  • Log into Homebridge Config UI X (This is NICE!) - Default uc/pw = admin/admin
    
    http://<ip address of your server>:8581

  • Couple of name changes in Configuration Reference Section of guide
    Note:  Service management is now via sudo hb-service restart/stop/start/logs instead of systemctl 

• Config using Config UI X installed above.
  The following is a blow-by-blow of our Smartthings and Nest upgrade - mostly for my sake!
  Steps dissected from https://www.npmjs.com/package/homebridge-config-ui-x

  • Log in via http://homepi:8581

  • Smartthings:  Step by steps below MAY still need cleanup ... MUCH has changed since I installed original (pdlove) HomeBridge SmartThings!
    Followed https://techtechandmoretech.com/guides/smartthings-homebridge/ 

    1. Via Browser:  Smarthings IDE @ https://graph.api.smartthings.com/

       • Log in to SmartThings IDE (POS!) - I had to use my Samsung credentials 

       • I ended up deleting old (pdlove) Smartthings App because Smartthings is CRAP!   AND it wasn't easy!  This may help - https://community.smartthings.com/t/this-smartapp-cant-be-deleted-at-this-time-because-it-is-installed-by-one-or-more-users/44845//

       • Go to MY SMARTAPPS and Add (upper right) NEW SMARTAPP

       • New SmartApp form:  Clicked FROM CODE tab and (blindly) pasted code from https://raw.githubusercontent.com/tonesto7/st-community-installer/master/smartapps/tonesto7/st-community-installer.src/st-community-installer.groovy

       • Hit CREATE Button, then SAVE and PUBLISH (for me) buttons in upper right of response screen

       • Hit APP SETTINGS button (still upper right) scroll down OAuth and Enable

       • Hit UPDATE button on bottom of screen

    2. On IOS (smarthings app has always been a friggin mess!) via NEW ST App
       OLD ST App BECAUSE THAT IS WHAT INSTRUCTIONS SAID!  (I made a mess doing it myself!)

       • <Follow instructions EXACTLY>

       • emailed (yeesh!) config.json snippet for ST

    3. Via SSH!  Update the config.lson file using texted pasted into email from IOS!

       • Found config.json in /var/lib/homebridge/

       • Pasted clipping from email onto jsonlint.com to doublecheck/validate 

       • Pasted clipping into /var/lib/homebridge/config.json

       • Had to empty and remove /var/lib/homebridge/accessories to get HB running
         I was getting error:  Cannot Add bridged accessory with same UUID read this
         https://github.com/luisiam/homebridge-cmdswitch2/issues/8

       • hb-service start (to get hb back up)

    4. Back to IOS (round and round we go!), Home App:

       • I deleted old home and added new one using UI QR Code to reduce confusion

       • Fumbled around in IOS Home App until I settled all rooms, devices and favorites

  • Nest:  Installed via Config UI X

    1. homebridge-nest v4.4.9 (Nest plug-in for Homebridge using native Nest API)
       Doc @ https://github.com/chrisjshull/homebridge-nest

    2. I still use Nest Account - pretty simple:  Access Token from home.nest.com/session
       (I'll update to Google account when forced to - this step is more complicated)

• Set up IOS phone via https://support.apple.com/en-us/HT204893

  • if you forgot your pin/scan code dig it out of systemd journal like I did
    
    sudo journalctl -u homebridge

• Debugging:  Troubleshooting Guide @ https://github.com/nfarina/homebridge/wiki/Basic-Trouble-Shooting

  • Running in terminal window is very helpful 

  • See Also:  Common Issues section in the README
    
    

Apple Home info @ https://www.apple.com/ios/home/

Some cleanup/updates:  A couple of new "Smart" things to incorporate into the home and some forced plugin updates.  Also removed the soundcard and cable to Bose - Airplay services no longer needed or used - HomePod sits right on top of Bose radio and sounds just as good!  ... notes/log

Failed attempted an update to Buster, ended up with some clumsy network issues during install, decided to simply update for now.

DietPi Tweaks/Updates

1. dietpi-update v8.13.2->v8.14.2 ... 

   • also did a -  apt upgrade Y

2. dietpi-software - couple of changes

   • Removed shairport-sync, no longer need to offer Airplay services. 

   • Added DietPi-Dashboard (backend only) - HomePi is now monitored via ServerPi on our network

   • Removed RPi-Monitor - replaced by Dashboard

3. dietpi-config

   • Disabled Audio - no longer needed

Homebridge 

• Update to v1.6.0 via UX

• Plugins:

  • Replaced Homebridge Smarthings with Smarthings Plugin a while ago.  It works and ia much simpler but some noticeable delays (slowly improving)

    • Updated new plugin to v1.5.0 - webhooks coming soon!

    • Uninstalled old plugin

Enough for now ... will do a rebuild using Bullseye in the spring, I think that should simplify this gizmo even more

Spring cleaning during the winter ... some leftover HomePi updates.  Should be good for a long while!

1. DietPi update from 7.5.2 to 8.1.2 ... no issues.  Just let dietpi-update do it's thing! 

2. Homebridge World

   • Homebridge update v1.3.6 to 1.4.0 ... no issues

   • Homebridge Plugins

     • HomebridgeUi update from v4.41.2 to 4.42

     • Homebridge Deebotecovacs update from v1.4.6 to 1.4.7 ... hmmm some odd chatter during update

     • Homebridge-hue update from v0.13.22 to v013.36

       • plugin recommends running on Node.js v16.13.2 or later ... Easy enough:
         From Homebridge "How to Update Node.js" article, did one of these:  hb-service update-node

     • Homebridge Nest update from v4.6.3 to 4.6.4

     • Homebridge Platform Wemo v3.3.1 - Replace with Homebridge-wemo v4.7.0

       • Platform Wemo was deprecated/replaced quite a while ago but w/out auto migration.  Just hadn't taken time to deal w/ ramifications of automations and such - some old/original smart-stuff here

       •  Step-by-step based on info @ https://www.npmjs.com/package/homebridge-platform-wemo

         1. Backup Homebridge (... Backup/Restore)

         2. Saved a copy of json from HB Config editor (not much there)

         3. Disabled current Wemo-Platform Plugin and restarted HB

         4. Uninstalled Wemo-Platform Plugin 

         5. Installed homebridge-wemo Plugin and accepted config as presented (json looked just like old)

         6. Restarted HB  

         7. Had to move Wemo stuff to correct room assignments and re-setup Automations ... not too bad

     • Homebridge Bravia Tvos - v5.0.1 to v5.0.8

     • Homebridge Nest - v4.5.4 to v4.6.4

     • Homebridge Smartthings - v2.3.8

Loooong time since last  update

1. DietPi update from 7.0.x  to  7.5.2 ... with one little bump in the road ...
   Repository 'http://raspbian.raspberrypi.org/raspbian buster InRelease' changed its 'Suite' value from 'stable' to 'oldstable'
   To fix, did one of these:
   apt-get update --allow-releaseinfo-change
   ... Then let dietpi-update do it's thing.  All else seemed well

2. Homebridge Update

   • Homebridge now v1.3.4

   • Some of the Homebridge Plugins were complaining about needing Node.js v14.17.2 or later ...
     From Homebridge "How to Update Node.js" article, did one of these:
     hb-service update-node

   • Homebridge Plugins

     • HomebridgeUi - no issues going to v4.41.2

     • Homebridge-hue - no issues during update, now v0.13.22

     • Homebridge-platform-wemo - project apparently moved to homebridge-wemo, but will change some other time.   No update issues, now v3.3.1

     • Homebridge Bravia Tvos (not used) - v5.0.1

     • Homebridge Nest - v4.5.4

     • Homebridge Smartthings - v2.3.8