- 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.
The modular phone was a nice dream but IMO a fairytale dream, even Apple have had problems fitting all the needed stuff together so good luck with a Lego phone except if it’s the size of a brick.
Now it’s probably the time for a linux/free/foss phone, as IMO they start to be both standardised and actually quite enough for the moment;
My old Xiaomi 9 pro that goes used for 80€ used in mint condition has 6GB RAM 128GB storage, SD card, octo core CPU etc. That’s close to my penultimate PC. The next next next version (Xiaomi 12Pro) has about the same specs except the camera stuff.
That’s when FOSS people can start to dig into stuff, not when specs changes crazily every year.