I’ve had this exact problem with x2go and xfce for the last month on my VPS. Though I’m not using Manjaro specifically, but just pure ArchLinux.
So I’m guessing it does have something to do with xfce4 and ArchLinux and an update to one or the other in the last month the started causing this problem.
EDIT: I’ve narrowed it down to the libwnck3 library. Specifically version 43 of that library that causes the problem. If you downgrade that library to the previous version of 40.1, x2go will start working again. And apparently it’s already been reported at the libwnck3 gitlab. Unable to post a link, sorry…
Not sure why that didn’t come up when googling for the problem in the first place. Would have saved me a few hours of head scratching lol 