During the last two SpamSieve updates (2.9.41 and the previous one), after installation, the “Make sure that Spamsieve’s Apple Mail plug-in is enabled” message appears and cannot be dismissed.
Clicking on either Quit or Continue has no effect, and the window remains “stuck” above everything else on the screen, requiring me to restart my Mac. I’ve used SpamSieve for many years, and this has never occurred until these last two updates. I’m running macOS 11.1 Big Sur.
When this happened with the previous SpamSieve update (within the last week or so), I took it in stride. But since it happened again today with 2.9.41, I had to report it.
I have a screencast of this behavior I can provide, if needed.