Craig Federighi Said himself that they don’t boot other operating systems. Could you link the talk where they said it can run binaries not signed by Apple? The only thing I could find is where they still allow you to boot older versions which they don’t let you download anymore. To keep the actual mac experience.

It's because they don't want to support drivers for other OSes.

See this WWDC session: https://developer.apple.com/videos/play/wwdc2020/10686

and this manpage: https://pastebin.ubuntu.com/p/RwcT8stYMY/

Can’t find anything in both documents which allows booting of non Apple signed Software. The only thing I See there is something like SecureBoot on PCs, where Apple would need to sign your boot loader in order to be able to boot it.

--permissive-security is the setting that you want. You are then able to enroll hashes of unsigned kernels with kmutil.

Kmutil is only there to load kernel extensions? Or did that change with Big Sur?

It changed. You use kmutil create to create the artifacts and add the hash to the Secure Boot policy. (--help at https://pastebin.ubuntu.com/p/mN3Z2kfJWy/, no manpage)

TIL this has a man page

I haven’t watched anything. Are you saying you can boot another OS? Can you point me to where I can read or hear more about this?