Having error when open any website

Is your device intentionally configured to use a proxy?
You can disable a proxy for a WiFi connection in system settings, networks and connections, WiFi, press and hold network name, edit, use proxy.
If the problem occurs on mobile data, then check with your service provider what the correct APN is, and verify in system settings, networks and connections, mobile network, APN.
It might also be possible to get this error if you are using a VPN and there is something wrong with it.