Apple Watch SE doesn't open Activity, doesn't show rings

My new Apple Watch SE doesn't show rings, steps, etc. It won't open the Activity app. After I switched my watch off and on, the app doesn't even show up in the list with all apps.

Things that I did/checked:

• both iPhone 11 and Watch SE run on the latest software
• unpaired, reset Watch, paired
• In my Watch app on my iPhone, settings, Activity, everything is 'on'
• iPhone - settings - Privacy & Security - Motion&Fitness - Fitness Tracking is on

I know that my Watch is in fact counting steps and everything, since when I open the Health app on my iPhoneI can see the 'Activity'.

[Edited by Moderator]