Fix ‘Import OS Updates’ Notification Won’t Go Away at Login on Ubuntu 23.10

I upgraded to Ubuntu 23.10 and, after a firmware update, I keep having an "Important OS Updates…" notification showing at every log in. I keep dismissing it, but it still shows up every time I log in.

I tried disabling notifications entirely in the settings for several applications (Ubuntu Software, Snap Store, Portal, Snapd User Session Agent, Evolution alarm) without success. I also read here that I could remove the file /var/lib/PackageKit/offline-update-completed, but there is no such file. With locate, I also tried to find any other file with completed in its name, but found nothing relevant.

It's not a big deal, but it's getting really annoying.

Any idea?