Unattended Upgrades - could not be installed automatically

Solution 1:

I eventually found the pin in /etc/apt/preferences.d

ls /etc/apt/preferences.d
cuda-repository-pin-600

Which seemed to be leftover from a cuda install I didn't really need. So I purged the cuda install, and removed the pin.

sudo apt purge cuda*
sudo rm /etc/apt/preferences.d/cuda-repository-pin-600
sudo apt autoremove
sudo apt autoclean

And then was able to update the (still installed) drivers using unattended-upgrade

sudo unattended-upgrade -d

after installing the driver updates and rebooting, nvidia-smi still works