I'm running VirtualBox 6.1. After the upgrade to macOS Monterey, my VM's fail to start up with the error message

Kernel driver not installed (rc=-1908)

I tried reinstalling VirtualBox and, while that worked at the moment, the problem began again when I turned on my computer the next day.

Based on similar questions on this site, I checked System Preferences -> Security & Privacy. However, there's no pending request from Oracle.