In the meantime, I activated the 5G option with Yallo, which costs extra. That's the only way 5G works. It works well with this Nokia. Coverage from Sunrise is mainly in cities. In the vicinity of 5G cells, the speed is great. Further away, however, it decreases and a connection doesn't necessarily work in the house.

I have Yallo and it's on the Sunrise network. So far I haven't had any problems. Phone calls and internet work fine with LTE 4G. I have never been able to see if 5G works as well. I may not be in a covered area. I wonder if it works with Sunrise and not with Yallo. Would be interesting to know. WiFi calling does not seem to be switched on either. With the Samsung S20, it works with Yallo, so I conclude that this device does not support it.
Otherwise, the usual things are working fine for me so far.