In a last ditch effort to reproduce, I just tried 7.4.1 on Bug Sure 11.2.1. Worked fine. I thought maybe there was some odd build issue between 7.4 and 7.5 that might be causing the issue, but that doesn't appear to be the case either. The Mac client has been 64-bit for years now, so I wouldn't have expected that to have changed but it was worth a shot.
What is the specific Mac model you're using? I'm using a 2018 Mac mini.
[EDIT] - sorry, just reread the first post and it looks like you have the same Mac I do. It's got to be something environmental on your Mac. But I can't think of anything else short of starting over which, given your internet, is likely not really an option for you. Do you have any other apps that have tables like this where you can do in-line table cell editing? The variable window is the only place in our UI where you can directly edit values in-line in a table. I'm wondering if any other apps are having the same issue and you just haven't noticed.
BTW, this is very reminiscent of issues we've seen in the past with VNC/Screen Sharing. Obviously this isn't the issue, I just find it interesting that it's similar.