When I don't use my iPhone, it disconnects the Wifi

Hey!

Recently, my iPhone started doing weird things with the wi-fi. I connect to my wi-fi early in the morning, but when i dont use the phone, it disconnects. And it keeps doing it every time. When i put my phone down, and then pick it up, it disconnects from the WiFi. And my cellular data is on, so it starts using cellular data. Turned off cellular data but it kept doing it. It is really annoying. I have an iPhone 8 A1905 and the latest iOS 13.6 is connected. My WiFi doesn’t have any specific blocking, or anything else. Any advices to stop this?

thanks

[Re-Titled by Moderator]