The tooltip vs notification count mismatch seems to be a consistent problem:
there were no updates available initially
sometime today 11 updates were available: a notification popped up saying so and the tooltip showed 11 updates available
now tooltip says 12 updates, but there were at least 2 notifications already still showing 11 updates
edit: When I (partially) update the system, the number in the tooltip will correctly show the remaining updates as available while the notification still insists on 11 updates being available.
@philm or anyone: could you update pamac-tray-icon-plasma with the latest commits in order to test if the issue is indeed fixed? Pushing the build files (PKGBUILD and any other files needed) on Gitlab would be great too, while you’re at it.