Still broken, but confirmed the workaround from the OP does work

I was able to work around without deleting preferences—use the full screen button in the title bar of the app window to go into full screen mode (it will look broken). Then quit with command-Q. On relaunch you should hopefully be in full screen mode!

same issue for last two weeks after upgrading to Sonoma 14.2.1 please fix!

Same issue. Critical issue. Literally cannot play the game until this is fixed.

Yeah I just sold my incredibly slow 2016 Macbook Pro, where the game worked perfectly in both windowed and full screen, for a 2023 M2 Macbook Air. Arena is unplayable on this computer. The edges of the game are completely cut off and there is no way to reformat the resolution. it only gives one option. PLEASE FIX!

Brand new M3 Max macbook and I also can't manage to login or play.

This worked as a solution for me, too! However having to play full screen only is quite annoying... Really needs to be fixed, please!

I have the same issue. Cant play the game right now :(

I have the exact same issue !!! Please do something thanks. The game is unplayable like that

same issue here! sonoma 14.2 on a brand new 14in macbook pro w/ m3 pro chip. just adding here for weight.

If deleting your preferences isn't causing your client to load in Full Screen mode the next time you launch MTGA, then perhaps you are launching it from the Epic Games launcher? Or Steam?

If you're launching from Epic Games, you can specify command-line arguments per the instructions here to force Full Screen mode on launch:

https://www.reddit.com/r/MagicArena/comments/nxqp6q/macos_users_here_is_how_you_get_fullscreen_and/

I don't use Steam, but I would bet you can modify the command line arguments there in a similar fashion.

Same here:
Model Name: MacBook Pro
Model Identifier: Mac14,9
Model Number: MPHE3LL/A
Chip: Apple M2 Pro
Total Number of Cores: 10 (6 performance and 4 efficiency)
Memory: 16 GB
System Firmware Version: 10151.61.4
OS Loader Version: 10151.61.4

Brand new M3 Pro MacBook Pro, same issue. Reinstalled Epic and Arena on a brand new machine- no dice. No inputs, can't get to fullscreen because the program freezes and requires a force quit. Please fix ASAP!

same problem on Mac Studio. can't click anywhere and can't quit application

Same issue. Solution posted here has not worked.

This is happening after Mac OS upgrade to Sonoma. Client is broken on Sonoma 14.2

same problem. Started after update to Sonoma 14.2.
The suggested fix doesn't work for me, the game client starts in window format.

The game is completely unplayable now. Workaround doesn't work on my machine as it still opens windowed.

Too bad nobody works at wizards anymore to help fix this...

M2 2023 MacBook Pro 16" Max running Sonoma 14.2

Game won't register any mouse clicks, neither trackpad or external mouse. Did complete reinstalls twice already.

2023 M2 MacBook Pro 14"

Unfortunately, the workarounds seen here don't work for me - I've got a widescreen monitor, Arena doesn't/can't launch in full screen.