WiFi goes on/off on iPhone without WiFi problems

Hi, for the past week or so I’ve experienced the following problem with my iPhone 8 Plus: the wifi keeps switching on and off. It’s on for maybe a split second before it turns off again and it stays off before it connects to the wifi for another short moment. I thought it had to do with our router yet every other device in my home has perfect wifi, including my MacBook. The same problem occurs on other wifi-connections and then it is only my iPhone having that problem, too.

It is incredibly frustrating because I go through my data really fast like this and can’t do anything on my phone properly because the wifi shuts off within a minute again and only connects after like, 3 minutes. My iPhone is completely up to date and yes, I have already tried to reset the network settings but the same problem kept occurring.

I hope someone knows a solution.