Connection wizard failing

Hello there!

Got a new Mac mini (2018, running Catalina 10.15.3) for work, and am trying to sync to our Nextcloud, but the following is happening:

  1. Enter our server address and click Next

  2. A white box flashes for a split second, then the Connection Wizard window just looks like this

Any advice on what to do to fix this, or angles to look at this from would be greatly appreciated!

Thank you.

When try a second/third/fourth time I can see that the expected next screen about requesting permission now loaded instead of the white box, but it’s only visible for the split second, then it’s as if the whole box ‘jumps’ up to just be that little blue bar poking down from the top of the window.