I've had the Galaxy S20 5G for about 2 weeks now and have had this problem from the start. My apps will not use wifi. I can only use my apps when wifi is turned off and my phone is using 5g only. I can use the internet on wifi and sometimes I can use the Google Play Store on wifi (but not always) and none of the apps downloaded from the Play Store can use wifi. I talked to a Samsung rep who told me to go to the Mobile Data screen and look for a setting called "Mobile Data Only Apps" and turn it off. I do not have this setting on my phone. It is nowhere in my settings screen. He suggested at the end to do a complete factory restore and I did. Still no setting and still having problems with my apps using wifi. My kindle in particular is the worst. I have to have 5g turned on and can only download 1 book at a time or it all fails. Is there anything else I can try?
Short answer - disable ipv6 on your home network.
I had the same issue on my S20+, but it didn't affect all apps. When I first got the phone about 3 months ago, I discovered that some apps NEVER worked with wifi, only with the mobile network. Some apps worked perfectly on either network. And some apps would use wifi for a short time and then stop. If I turned off wifi on the phone and ran the app on 5g for a while, I could turn wifi back on and the app would continue to work ... until it eventually stopped again. I was starting and stopping wifi on my phone several times a day depending on what app I was using. It was extremely frustrating.
After a LOT of research, I discovered it had something to do with ipv6. I could go on and on about all the weird combinations I found of what apps and networks worked/did not work together. It was almost a game with my friend and her new iPhone and me with my new GS20+ to see what apps worked where.
The fact is it's not JUST a Samsung issue. It has to do with how a number of things come together when ipv6 is enabled:
- the mobile device
- the ipv6 configuration on the wifi network
- how the app handles network traffic, and ultimately the responsibility to fix the issue lies with the app. My favorite example was the Home Depot app. It was one that worked on 5G but not on my home wifi or even the wifi in my local Home Depot - I loved the irony. They have since fixed their app.
For me, the best option was to disable ipv6 on my home network. Now all my apps work fine at home which is where I spend 99% of my time these days. Maybe the app developers will have this mostly sorted by the time we're all free to move about the planet again. #PandemicLife