That’s possible on very few phones these days. Only a handful of OEMs still ship phones that can be bootloader unlocked at all (at least in the US), and even several of THOSE require phoning home to the OEM to get an IMEI-dependent unlock key to pass to fastboot.
Source: 7 years of running deGoogled Android phones and 11 years of running ROM’d Android phones before recently moving to iOS and giving up.
Just found this [0] in another thread. Some few allow no unlocks, most allow them under certain circumstances. Some few without a waiting period or additional sacrifices.
So not as great as I thought, but also not as bad as you made it seem ;)
Two of my deGoogled Android phones were Pixels (4a and 7a) and one was a Nexus (6p). I know them well, though I never ran Graphene on them.
Pretty sure I read Google was no longer going to publish device tree sources for Pixel phones, which will make ROM development for them significantly harder, whether or not the bootloader is open.
Source: 7 years of running deGoogled Android phones and 11 years of running ROM’d Android phones before recently moving to iOS and giving up.