I’m in the same situation. This seems to occur only with AVM routers as documented extensively here. No other devices have this problem connecting to AVM routers. I and others have contacted support many times to no avail, they’ll just throw standard text blocks at you.
I too will probably get another phone. I don’t want to (mis-)configure my own router just to make it compatible with the FP3’s broken WiFi implementation. Also I often connect to other AVM router networks and I certainly won’t ask the owners of these routers to change their configuration for me.
I was planning to keep my FP3 until it stopped being supported. But I won’t keep using it if such an important part of its functionality is not working.