After updating from 3.13 to 3.14, the program forgot the settings for proxy authentication and cannot be made to connect to the server even by using “manual proxy settings” instead of “system proxy”.
When you freshly reinstall version 3.14.x, the proxy settings are not requested at all.
Uninstalling and reinstalling version 3.13.x makes the client operational again and ready to connect.
In such a case where something breaks during an upgrade, you can directly report it to the developers on GitHub · Where software is built