All you said was correct. And I'm using systemd.
If I press e on the boot loader choice, then put nomodeset at the end of the entry, I'm able to have display, but it looks pretty choppy compared to when it boots normally without issues without nomodeset.
I have a 6900xt GPU, and
/lib/firmware/amdgpu/
Is missing a driver for the "navi 21" codename / family series. I don't see it in the full Git downloads either.