>Very easy if you have an Android phone Very easy if you have an Android phone from the correct manufacturer that and it's popular enough to have custom roms for it or you know how to port custom roms to other devices*

Nope, nowadays any recent-ish Android can receive custom ROM very easily, using GSI.

But the restriction is that many OEMs and/or carriers forbids bootloader unlock.

If you have Android, you have to have an excessive number of stars aligned just right for a successful OS replacement. On x86, the replacement involves toggling some firmware settings, rebooting, and using a point and click installer. On Android:

1. Have bootloader unlock available via official channels. If you are in the 1% with a supported phone variant, congratulations. Service box unlocks, while often possible unofficially, rarely result in a critical mass of developers that's needed for the next step.

2. Have a ROM ready to go. If lucky, it'll be Lineage OS. If less lucky, some unofficial build of Lineage OS with potentially some hardware not supported (but there's hope!). If you are really unlucky, the phone is so unpopular that a ROM developer hasn't taken enough interest in it to produce a usable ROM.

3. Flash the ROM, keeping all idiosyncrasies of the particular hardware in mind. Hope you got the right partition table/kernel/bootloader/ fragile fragment, because if you flash the one meant for GEX5546ab on a hardware that corresponds to GEX5546cb, you just killed your phone. Run through contingency procedures for unbricking the phone in case you need them.

4. Congratulations. You now have a firmware that works better than the factory OS, but they also happens to potentially not support small things like Bluetooth or the camera blobs. You may get support in 2-3 months, hopefully. Your secure enclave keys are also gone, so bank apps will be suspicious and Netflix will refuse to serve higher-quality content.

>1. Have bootloader unlock available via official channels. If you are in the 1% with a supported phone variant, congratulations. Service box unlocks, while often possible unofficially, rarely result in a critical mass of developers that's needed for the next step.

Untrue for most of the phones on XDA, S3 was the most popular android phone and came locked.

>2. Have a ROM ready to go. If lucky, it'll be Lineage OS. If less lucky, some unofficial build of Lineage OS with potentially some hardware not supported (but there's hope!). If you are really unlucky, the phone is so unpopular that a ROM developer hasn't taken enough interest in it to produce a usable ROM.

Luck to me is more than LOS, its the bare minimum, but I have gotten unlucky with non popular phones. Not hard to look at roms when you see if you should root or install custom bootloader.

>3. Flash the ROM, keeping all idiosyncrasies of the particular hardware in mind. Hope you got the right partition table/kernel/bootloader/ fragile fragment, because if you flash the one meant for GEX5546ab on a hardware that corresponds to GEX5546cb, you just killed your phone. Run through contingency procedures for unbricking the phone in case you need them.

You could just run Halium to run Linux with all drivers, or use chroot to have linux in it too. Safety that existed since 2012 prevented me from ever having a single issue like that, and I never bricked a phone with over 20 flashes.

>4. Congratulations. You now have a firmware that works better than the factory OS, but they also happens to potentially not support small things like Bluetooth or the camera blobs. You may get support in 2-3 months, hopefully. Your secure enclave keys are also gone, so bank apps will be suspicious and Netflix will refuse to serve higher-quality content.

This was occasionally true before 2017. All new phones have mainline linux support. https://www.computerworld.com/article/3306443/what-is-projec... https://www.xda-developers.com/android-project-mainline-modu...

Basically, if you spend 10 minutes looking up relevant information, buy a popular phone with good support and you will face 0 problems. You are making a mountain out of a molehill.