This has been an ongoing issue since the May update. June did nothing for the issue. I'm sure that if people didn't have unlimited data plans Samsung would be mobbed with complaints. I've tried the "fixes" that don't work. And NO it's not my router as the laptop and tablet (running an older version of Android) connect to the wifi with no issues. Instead of having customers jump through hoops to fix it, why doesn't Samsung fix it with a patch. Our 2 S21's worked great until May. We never needed a big plan as we always had access to wifi, but now coming in from a walk, you have to be vigilant about turning on the wifi. I've had Samsung phones for years, but their lack of addressing customer issues is showing like a billboard. Something different for the next phone.
There is a WiFi option to turn off/on WiFi automatically when in certain locations. I have found it to be finnicky and turned off the feature. WiFi -> Advanced -> "Turn on Wi-Fi automatically"