So I thought to check how it looked on another machine. I haven't messed about too much with this Windows 11 install, pretty much just installed chrome & let it sit there. This installation also has the ribbon above the menubar..
However, Groupy 2 installed reasonably well. At first it looked like it didn't take, but after I'd closed the tabs that already existed before I rebooted, it seems to be working just fine.
Unfortunately, this is just on a partition on a dual-boot machine as a test installation, so there's not really any of my other software installed to give me any idea of what might be messing things up on my main machine...