Ironically, Google's own Pixel line is the only reliable source of phones I know of that's both unlockable and relockable with your own keys. The latter is an important feature that even the "hacker friendly" brands like early OnePlus skipped out on.
Hopefully the hardware vendor GrapheneOS is working with can add a second product line to the list.
Some of the ones that seem unlockable are actually not unlockable in practice. Like Xiaomi which provides an unlock option that doesn't work unless you work for Xiaomi.
Hopefully the hardware vendor GrapheneOS is working with can add a second product line to the list.