Well the install per user doesn't show native notifs either now. Probably broke something or it picks leftovers stuff from the registry. Oh well.
We probably need a cleaner sort of app for these situations that purges all traces of an installation.
Weirdly enough, in the old OS install, same version, but upgraded over 2-3 years, notifs worked OK, but this fresh Windows/Vivaldi combo broke the notifs.
"fixed" it
Went through the registry and deleted some related Vivaldi stuff, including an entry that specified the location of the install on Program Files.
Installed per user in that annoying AppData\Local folder (whyyyyyy when we had Program Files for ages) after a reboot and now notifs are OK.
So location of the install seems to be the issue? Seems to be required for Win11 to pick it up like this:
c9a905a2-55d3-4076-8288-3fe61d773a97-image.png
Without this, you are not gonna get native notifications.