Craig Federighi confirms ARM Macs will not support booting other OS's (youtube.com)

I think I jumped the gun with the title. It appears that you can still turn off secure boot entirely on ARM Macs, per this WWDC video https://developer.apple.com/videos/play/wwdc2020/10686/

I'm doubtful it would be possible but if there was an AppleTV sized MacMini with the Apple ARM chips they would make one hell of a home headless server if you could install Linux on it natively.

We have to wait and see.

Back in my day they used to add features in new versions