Hi
yesterday I updated my Fairphone 4 from iodeOS 5.7 to 5.8 and restarted.
Since then I had no sound through my speakers: no music, no notifications and (as I experienced this morning) no alarm clock 
Sound through Bluetooth worked fine.
The problem resolved after another restart.
So no help is needed unless the issue arises again.
I am just putting it here as an heads-up for the developers and a reference for other affected people.