I did see a post here in Docs Q&A one or two weeks ago, where someone claimed that a specific update to Window 11 Insiders broke SSMS. I don't run SSMS at all on Windows 11 (yet), so I cannot verify. But you could search backwards to see if you can find that post and which KB you should try uninstalling. It was a recent update, as I understood it. (Something about tabs in Windows Explorer as I recall.)
By the way, thr most recent version of SSMS is 18.12.