AirPlay to Apple TV not displaying at full 1080 resolution?

Question

I can successfully AirPlay from my M1 MacBook Pro to my 4k Apple TV connected to a 1920 x 1020 display... but I can only get a resolution of 1280 x 720:

When I'm not AirPlay'ing and just using the Apple TV as one would typically use an Apple TV, I get full 1080.

How can I AirPlay at full 1080?

Answer 1

Hold down Option and click the Scaled button. Like magic, a whole bunch of new resolutions appear:

I found this here: How To Set Custom Resolutions For External Displays In Mac OS X

I have no idea why these resolutions don't appear initially... especially in my situation where 1080 is the native resolution.