Wifi repeatedly connects and disconnets since iOs 18.1

Hi! Since I updated my iPhone 13 to iOs 18.1, I have constantly issues with my Wifi. It connects for like 5 seconds, then it disconnects, and then it connects again for 5 seconds, then it disconnets, and so on. I already tried:

• restarting my iPhone
• forget Wifi and try to connect again
• turning off Wifi assistance

... and all of the above didn't work.

It is really frustrating, because my Wifi actually stops working when it disconnects (not like it is a little bug that only the symbol changes from Wifi to 5G and back).

Can anybody help me please? Thanks!