After Update iPhone to latest iOS 14.0.1 Suddenly all connected WiFi network have issue. All web sites show "Safari cannot open the page because your iPhone is not connected to the internet".

This is weird because the URL is the internal server like 192.168.0.108. The target URL is a metro server running on my iMac and i can access on my android device. Metro Server is React Native development server.

At the times, I was start studying React Native， When debug on iOS device their are difficult to connect and debug on device i still think this is React Native issue.

I try to visit apple.com on browser also same issue. reconnect WiFi again but same result, Even restart the phone also same.
This iPhone is one of my developer device inside device are no any other apps install. Few day ago i have update the iOS to 14.0.1 So i thing the updated may cause some issue.

I can find many user also have same problem on apple developer forums almost can confirm is the 14.0.1 updated cause the WiFi Internet Issue.

So I check if any new updated to solve the issue. But currently is no any new version to updated and solve.

After some try i discovery a solution.
Removed WiFi profile and connect again

Settings > Wi-Fi > Select the Wi-Fi you connected > Click on Forget This Network > Reconnect the Wi-Fi Again.

There are many problems with recent iOS updates.Hopefully Apple can make the updates more stable and safe before release.