- Unlock bootloader (depending on vendor, you have to do an online verification),
- flash a recovery.img,
- load into recovery mode (which, depending on the phone, might need extra work)
- wipe some caches,
- select new os/rom image,
- pray it doesn’t brick your phone.
You’d think someone would’ve learned a thing or two from the easy graphical installations linux and even windows have been offering since the late 2000s.
Very few people try to change their OS because it is difficult. If it was easy, more people would do it. Most people SHOULD NOT do that. Apple would have to triple their tech support staff just to keep up with the people who don’t understand their new OS, or complain about regular features not working like they used to, and those are the ones that don’t brick their phones while just poking around in some settings they don’t understand.
They should ease off a little with allowing it, but pretty much only those who REALLY know what they are doing can’t pull it off.
That doesn’t explain it, especially because they can very well say that the end user’s warranty void if they uninstall the packed in OS