Assuming you are running 13.0 Current, and already put the entry in
/etc/rc.conf:
kld_list="amdgpu" #Yes, no path needed, just "amdgpu"
Having done that, try this in /boot/loader.conf
hw.syscons.disable=1 # then reboot
I'm not the expert here, but the cause is what I might call a "framebuffer
Having a Raden 240 (sometimes 250) and an older AMDGPU. The older card is
deactivated in BIOS but it is been found by the X -configure problem. X server
did start one time with -config /root/xorg.conf.new, copied to /etc/X11/
xorg.conf, never got back any "blank black grafic" screen. Rebuilt new
