iMac of the late 2013 has M1 chip? or you have new MacBook Air with M1?
In any case, join forum and create topic there (in bug reports). Maybe more Mac users will see your topic and will help you.
I am not Mac user and i don't plan to buy Mac anytime soon. On Windows i have option to build for Mac and till now everything was working fine. Maybe in Unity 2020 they changed something when they added option to build for Apple silicon.
When more users will provide all info about problems running game on Mac, then i can create topic in unity forum and one of unity engine devs may help.