Bought a S21 a few days ago. In general, it works as it should. I'm having the same problem with several apps and am starting here because of the broad nature of my problems. Before I start, I also have a Galaxy watch3.
One at a time . . .
I have 9 Ring cameras - If I get 10 Ring notifications a day, 8 give no audible notification nor popup on the phone/watch. Of the two notifications I get, one is delay 20-30 minutes. (No times I give are exaggerations)
Reminder app - NONE of the reminders workas they should. Most give no audible tone and no visible notification on phone or watch. Those that give notification are delayed up to 2 hours.
Gmail app - works better than others, but still get emails with no audible notifications and, at times, get 5-6 at once.
Location app - no notifications work
Notification History (that's the name of the app) - hasn't logged a notification in 2 days
Step count - will go 2-3 minutes and not record a step. When it 'catches up,' I can 'lose' as many as 600 steps.
Accuweather widget - local temp on widget NEVER updates. Have to tap the widget to get it to open the web site in order for it to update.
I have watchMaker on my phone/watch. Temps on the watch face don't update until I go to WM on my phone, go Settings>Weather?Update.
FWIW, phone calls work. SMS works.