Turns out I forgot the AGKTier2 lib is open source.
I did it myself, here's a dirty port of AppGameKit for Apple Silicon. Works like a charm ! Performance improved by up to 30% in the various Tier 2 demo I tried.
Here's the repo: https://github.com/Kakise/AGKTier2onAppleSilicon
UPDATE: Added an updated template that compiles perfectly on Xcode 12 M1 !
If someone on the staff wants to get in touch to have more info about how to port it I'm down with it. AppGameKit Studio isn't open source afaik, so I couldn't look into it much but I already started changing memory management on the studio interpreter to make it compatible with Apple Silicon