I am trying to use screen mirroring from my MacBook to my iMac, but when I click on the + in the Displays settings menu only the Apple TV appears... It's the same the other way around. the MacBook is running MacOS Ventura and the iMac runs Catalina, but would this really be the issue? Both are compatible with airplay and screen mirroring after all.
MacBook Pro 14″
Macs have been able to use AirPlay to display things on Apple TV set-top boxes for a while. But AirPlay to Mac – where another device gets to display things on a Mac's screen – is a more recent feature.
It sounds like your Mac might need to be running Monterey or later to take advantage of it.
System requirements for Continuity on Mac, iPhone, iPad, and Apple Watch - Apple Support
https://9to5mac.com/2021/06/20/macos-monterey-airplay-to-mac/
Macs have been able to use AirPlay to display things on Apple TV set-top boxes for a while. But AirPlay to Mac – where another device gets to display things on a Mac's screen – is a more recent feature.
It sounds like your Mac might need to be running Monterey or later to take advantage of it.
System requirements for Continuity on Mac, iPhone, iPad, and Apple Watch - Apple Support
https://9to5mac.com/2021/06/20/macos-monterey-airplay-to-mac/
Screen mirroring between MacBook and iMac
