danieldesigner4041 wrote:
Can I use my 2019 iMac as a monitor for 2020 MacBook Air M1?
No. Target Display Mode went away when the first 27" 5K Retina iMac came out in Late 2014. Your 2019 iMac does not support it. On top of that, your M1 MacBook Air doesn't support using ANY iMac as a Target Display.
See the bad news in: Use your iMac as a display with target display mode - Apple Support
Your Macs are recent enough that if they're running Monterey or later, you can use either one as an AirPlay Receiver for AirPlay to Mac. AirPlay is not nearly as good as a hardware connection to a real monitor, or Target Display Mode connection. The resolution choices are very limited and there may be artifacts and lags; but given that you already have the Macs, it costs nothing to play around with it.
System requirements for Continuity features on Apple devices - Apple Support
Set up your Mac to be an AirPlay Receiver - Apple Support
When I plug a Thunderbolt cable in both computers, and hit Command+F2, nothing happens whatsoever. Do I need some sort of adapter? I don't see where there is anything else to plug into my iMac.
Command-F2 is what you'd use to get into Target Display Mode on an iMac that supported it. But your iMac does not support it.
There's Luna Display (Astropad), but it's not the same as a hardware connection to a real monitor, and it would be awkward to use on a MacBook Air with only two USB-C (Thunderbolt) ports.
(I plan on updating my MacBook to a M3 fully loaded and use my iMac screen. I'd like to know if that's going to work or not.
It won't (see above).
