No Wi-Fi on Ps4 while the TV is on?

I have a problem For about 3 weeks now, in the afternoons when my parents watch TV on a Fire Tv Stick, I have had very strong lag while playing on my PlayStation. We have a FRITZ! Box 7560 and a 50k line according to PlayStation come to 30-40k which should be enough. However, once this Fire tv Stick is on, I can't play properly. We had a FRITZ! Box 7590 bought for the test and it still didn't work! I think something can definitely be regulated with the settings in the FRITZ! Box, maybe someone knows.

You can add the PlayStation to the prioritization list

I've tried that but unfortunately that doesn't change anything, even restarted the router, etc.