Alan and bug 899086, Please try testing if this situation is improved or fixed in debian testing (to soon become bullseye) images, similarly to as you did before.
In fact the cdimage address you linked seems to be still exactly correct!. I'd like to see bug-report either closed or updated for bullseye. Given all the changes/massive improvements in amdgpu modesetting I expect the situation to be considerably improved, at least!. --Simon
