Problems installing CUDA drivers, "Package cuda-drivers is not available"

Hi folks, I’m new to CUDA and doing some testing on a DGX that has a clean Ubuntu 20.04 install. I’ve updated the signatures for the nvidia repositories, but despite following every guide I can find, including instructions on how to manually install the drivers I keep circling back to this error which I can’t solve.

$ sudo apt-get install cuda
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 cuda : Depends: cuda-11-7 (>= 11.7.0) but it is not going to be installed
N: Ignoring file 'cuda-ubuntu2004-x86_64.list.old' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'cuda-compute-repo.list.old' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
E: Unable to correct problems, you have held broken packages.

$ sudo apt-get install cuda cuda-11-7 cuda-runtime-11-7 cuda-demo-suite-11-7 cuda-drivers
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package cuda-drivers is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

N: Ignoring file 'cuda-ubuntu2004-x86_64.list.old' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'cuda-compute-repo.list.old' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
E: Package 'cuda-drivers' has no installation candidate

$ cat /etc/apt/sources.list
deb http://us.archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
deb http://us.archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
# deb-src https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/ /
deb https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/ /

$ ls /etc/apt/sources.list.d/
cuda-compute-repo.list.old   cuda-ubuntu2004-x86_64.list.old   dgx.list           dgx.list.save
cuda-compute-repo.list.save  cuda-ubuntu2004-x86_64.list.save  dgx.list.dpkg-old  graphics-drivers-ubuntu-ppa-focal.list

These are the recommended instructions. sudo apt-get install cuda does not appear in them.