Given some other experiences with amdgpu modesetting
problems, and looking at this bug, I would say:-
1) Please try updating all packages and reboot and
try again, kernel should be now 4.19.0-16
2) Secondly, enable backports
https://backports.debian.org/Instructions/
and then:-
apt-get -t buster-backports install linux-image-amd64 linux-headers-amd64
This should get you a 5.10 series kernel. My strong experience with
amdgpu has been that a whole lot of modesetting, sleep, etc etc.
issues are massively improved in 5.10 kernel series of late,
irrespective of the xserver-xorg version in use.
NB: At boot-time, in normal cases, GRUB menu should allow you
to 'select' which kernel you boot into i.e you should be
able to select between 5.10.0.bpo.?? and 4.19.0-16 kernel.
I note, the backports kernel is lagging behind a little,
hopefully 5.10.0-0.bpo.6 and 5.10.0-0.bpo.7 will come
out soon.
--Simon
