- 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.
It used to be easy… When people were actually making custom ROMs for everything and you could literally just plug the device into your PC and run a program to do everything. I don’t think there is anything inherently in most phones stopping this; it’s the lack of people developing custom stuff for every piece of hardware out there. Some phones do actively try and thwart custom ROMs, such as Samsung with their Knox bullshit, but most don’t need to; nobody is hacking them in the first place.