I just want to give a shoutout to justmoth's workaround - this was driving me a bit loopy but at least now it's fixable (for the time being)

Really awkward that there hasn't been any sign of acknowledgement or fix for this issue from GOG though

Edit: maybe I spoke too soon - it worked once but haven't managed to get it to work a second time. I guess I will continue to be driven loopy.

I had the same problem in a couple of Steam games and other platforms. The ideal is Contact support opening a ticket in mantis, they solved the problem for me without reinstalling anything.