You’re likely to hit the common problems porters face with putting Linux on an arbitrary ARM SoC. These chips have lots of integrated components on them, requiring device drivers that may not exist for Linux. Take the custom Apple developed in house GPUs for example. Good luck finding any kind of Linux device driver for those, open source or not. It gets even worse for things there isn’t even an external equivalent of, like the neural engines.

Even if Apple does nothing to stop you running whatever software you like on the device, you’re still likely to be out of luck. I wouldn’t be surprised if some enterprising folks have a good run at it, but it’s likely to be a massive undertaking.