On Ubuntu 20.04 Focal, I upgraded to kernel
5.4.0-42 (using the Software Updater GUI / apt) and my Nvidia proprietary drivers stopped working.
Rebooting to the old kernel (
5.4.0-40) yields a working system, so it is clear that the kernel update was the trigger for the problem.
I did all the usual things of ensuring that nouveau was blacklisted and updating ramfs. I also purged all nvidia packages from apt and reinstalled. No luck.