VirtualBox: kernel driver not installed (rc=-1908)

 This is deja vu - I'm sure of it.

 By now I've seen the pattern behind this error, which prevents a VM (mine's an Ubuntu 20.04) from starting.  It always happens after a macOS (host) upgrade, which would usually have a new kernel version I think, thus requiring the kernel extension for VirtualBox to be upgraded - at least that's my theory.  So I downloaded and installed the up-to-date version of VirtualBox.  The first time launching of the app after installation prompts an upgrade of the extension pack, which is handy!  I finished that, and hit the Start button.  Same error.  😢😢

What I forgot (not the first time) is this:

The OS automatically blocks the new extension until it's authorized here in the Security app.  I vaguely remember the VBox upgrade installation would remind me, but not this time at least.  Hopefully this has a better chance being committed to my memory after I write it down on a post.

Last thing to remember - restart the computer after the extension is allowed so it can take effect.  Then I'll have the sweet moment of finally getting back into my VM!