I too confirm the bug with my Debian testing setup and Linux 5.9.0-1. In
message #30 Rob points out that nvidia-kernel-dkms 455.23.04-1 works,
and I can confirm this too. You won't find it in unstable (this has the
same 450.66-1 as testing), but in experimental. Do not forget to install
all other nvidia dependencies also from experimental.
So for the time being: grab the whole nvidia files from experimental,
and then you will be able to use the 5.9 kernel. Guess they should
accelerate the propagation to unstable and then to testing pretty soon,
as the 5.9 kernel installed per default else breaks all nvidia owners/users.
Heinz
