On the official NVIDIA forum, an employee put out an announcement warning NVIDIA GPU owners that the Linux Kernel 5.9 and later is currently unsupported. It's worth noting they posted that in the CUDA forum, so other workloads like gaming may work as normal.
In the post they mention Kernel 5.9+ is currently "incompatible" with any of their drivers, and they're suggesting to wait until "mid-November" for a fresh NVIDIA driver update which is expected to bring support for it. They're "working diligently" to get ready to support it.
So what's going on? As it's quite unusual for such an announcement to be made. Well, NVIDIA don't appear to be saying in public why it's happening. However, we sort-of know and it's a complicated one that involves GPL licensing, Linux Kernel modules and Linux Kernel developers not being happy about how a patch was sent in by Facebook to the Kernel mailing list that would only work with the NVIDIA driver.
The result of the colourful discussion around it was a patch that was merged in, which mentions that it was designed to "prevent GPL shim modules that are used to circumvent _GPL exports" and that they will now be properly rejected.
The good news is NVIDIA are on it, and soon they will get a new fully-supported driver out. Until then, if you're on an Arch-based distribution, I can suggest trying out the NVIDIA installer from Tk-Glitch over here which seems to work quite well.