Outlook desktop won't open at all

A few months ago, something changed and I haven't been able to open Outlook for desktop since. I've been using it for years with some limited problems.

Now, I get the message attached - can't contact exchange server.

I've uninstalled and reinstalled and my outlook works on every other device - web, mobile, mail app - no worries. It's obviously something I'm just looking straight at but can't see.