I recently got my m1 macbook pro and running big sur 11.0.1 w xcode 12.3 pretty much everything works (with a few caveats) ! Here’s what I have tested so far:
Building the engine from source - Works
Remote compiling cpp ios projects from windows to the m1 mac - Works
Building and deploying ios projects directly from the editor on mac - Works
Compling and running cpp ios projects from xcode - Works but you need to do the fix listed here: Unable to compile with Xcode, Unreal 4.26, Big sur - UE4 AnswerHub
I am getting some weird graphical bugs in the editor however, see the attached screenshot. This was just the third person template with absolutely no changes. Oddly enough on the device it was fine. shrug.
Anyways I figured some people would be happy to hear that it basically works fine. Rosetta works well. I wouldn’t use it as my main dev machine but it works fine for a remote compiling workflow with a main windows dev machine.