Catalina login hangs when logging in using an account other than the main account

Mac mini running latest Catalina update

My son has an account on my Mac mini - I was logged into the Mac and my son logged in to his account while I was logged in. He’s done this hundreds of times with an issue but today he is getting the dreaded spinning wheel after entering his password. It’s been hung now for about 30 minutes.

I’d like to avoid rebooting the Mac if possible because I don’t want to lose things I was doing - is there any way to cancel his login attempt using the keyboard?

I should be able to log in remotely from another machine if that’s the best way to fix this - but haven’t tried it yet.

Thanks in advance