I've been dealing with this problem for months now since I got the s20+,
and have done all the requested attempts of rebooting phone, wifi, etc and nothing worked. I think I just figured out the problem as my phone had been working and not dropping the internet anymore. I found it by accident. Pull down the the screen to access the settings and select power mode. Uncheck limit CPU to 70% and accept. I'm sure it'll decrease the life of my charge, but so much better than constantly getting booted off my wifi, not to mention at work where I rely on being on wifi. FINALLY!! I hope this works for others and that's why I had to share!!
Here is the fix guys.
Go to wifi settings.
Tap on top right corner 3 dots
Uncheck switch to mobile data
I use my phone in my basement office with wifi and my router is upstairs but since I got s20 it frequently drops wifi all together even though its not that far from upstairs router. Due.to the option enabled as soon my phone gets weak signals from router it.drops the connection even though home router these days can adjust client if they go far.and put on better frequency.
No further drops and signals stable
Let me know if this helps
This did NOT fix it on my S20+........ but my problem was specifically that the WiFi on the S20 Plus, though connected with a strong connection to the WiFi router, would not communicate more than 15 minutes to an hour or so. Then it would just stop while still being connected. My solution:
....was to replace my 5 year old wireless router. I just went to Walmart and bought a new NetGear AC1600 for $85. Problem solved. No more WiFi drops by the S20 Plus. You can only mix old tech and new tech for so long I guess. :-) It has been over a week and I have had no further issues with the WiFi on the S20 Plus.