[2021] Playable on Mac?

The game ought to be playable on that hardware. It is and was mainly on intel video systems that there were problems.  

I can't recall ever seeing a Mac with dual video systems playing our games on the wrong one.

Are you having this problem right now?  

Please attach here your Documents/Paradox Interactive/CK3/pdx_settings.txt .
From your Documents/Paradox Interactive/CK3/logs/ folder, attach here system.log , error.log

Also in Steam please click on Steam-Help-System Info, and paste everything there into a text file and attach that here.  

That system.log shows the game is running on the AMD video system, as it should be.

I see you have Vsync disabled but no refresh rate cap. Probably best to enable Vsync, to make sure the game is not pushing the video system too hard.

Next I see your Mac desktop is at 1680 x 1050 but the game is at 2880x1800 in fullScreen. Does it help if you reduce that to the same as the desktop resolution?  

Don't blame yourself, that may have been the default for all we know.