Hello everybody,
I want to share how I solved the problem with notifications.
Before I go to the solution, I want to mention that "Reset all settings" helped me but temporary. So I tried different things like disabling Bluetooth and repairing/unpairing my watches, but that didn't help.
Then one day, during the app update, I faced the "storm" of notifications (100+ notifications appeared) that reached my phone at the same time. So I assumed that there's an app or several apps triggering the problem are being kicked from RAM/" push" listening during the update.
But after the "storm" the normal behavior hadn't returned, so I've started removing apps that were recently updated one by one, and voila, after removing one of these apps, I faced the notification "storm" again, but this time normal behavior persisted.
To make the proof, I tried to install/remove the app several times, and the result was positive all the time:
Installing -> enabling notifications for the app -> no pushes
Removing the app -> notification storm -> pushes are back
In my case, the problematic app was immobilienscout24.
I believe the easiest way to find the problematic app is to reset settings and then enable notifications for a bunch of apps, check if notifications are working fine, and enable notifications for another bunch.
Good luck!