Ok. So kept digging and got file sharing notifications to work. Still waiting for someone to share any thought for activity notifications email to work. Just for info in database role oc_activity_mq stays empty, no entry there at all.
Settings → Personal → Activity.
Check all the boxes you want to be notified for under the notification method you want.
At the bottom, set “send notification emails” to the desired frequency (as soon as possible, hourly, daily, weekly).
Also go into Settings → Administration → Basic Settings, and make sure that Background jobs is configured correctly and has a green dot. If they aren’t running, then it probably won’t send emails reliably.
Good luck with getting any kind of notifications with this service. People have been complaining about notifications for years now since 2018 and there has been NOTHING done about it.