No notification No sound alarm Apps

I don`t get any notification or sound from alarm Apps i download via F-droid.
I tried “simple clock”, “clock+”, “alarmio” and “alarm klock”, and gave them every permission possible, und activated the disrupt funktion for their notifications.

After downloading “simple clock” from google play, it worked out of the box.
Does anyone see my mistake ?

Duplicate post: No notifications No sound from Alarm Apps.