Until we have affordable fully open phone hardware specifications, the current phone hardware oligopolies will continue to gate keep with brittle proprietary drivers to ensure that people stay inside their walled surveillance garden.

Very very few existing phones allow bootloader unlocking and using your own keys, its why GrapheneOS only works on Google Pixel devices.

I imagine at some point even Pixels will stop allowing that.

There's a reason even GrapheneOS is looking to build their own phones. You pretty much need a published device tree and that's becoming rarer than hen's teeth in current phones. Even Pixel's are starting to get locked down.

That's hard to do given the driver issues, how locked down phones are, and the fact you're completely reliant on the benevolence of another faceless multi-billion (or trillion) dollar company.