"System Extension Blocked" message

I was just composing a mail message in Mail (the KM engine/editor were running in the background) and I got an odd macOS system message that I've never seen before:

System Extension Blocked
A program tried to load one or more system extensions that are incompatible with this version of macOS. Please contact "Apple Inc." for support.

I looked in both of the KM log files and saw no related message at the time I got this. So maybe it's unrelated to KM. But since my Mac has very little on it besides KM, which also has been recently patched, I thought I should report it. There's only a 10% chance it's related to KM, but I'm still going to mention it.

Oh wait. I just noticed a hidden window which was trying to update my mouse driver. So I'm 90% sure it's related to that.