FYI the issue I raised is a duplicate of this one and can be merged/closed:
https://phab.starma.de/T2299

I haven't seen this issue since the launcher update, and it seems like no one else has this issue, so this ticket can be closed.

I've just tried totally deleting my game folder and all related data, then reinstalling everything, the issue still persists. Files are attached, I hope someone else has some idea

vsync was not enabled. Still ignoring frame cap

I don't know about 'infinite', but I waited a couple minutes with it selected, and the program never came back into focus.

I just tried setting the frame cap to 30FPS, it didn't improve anything.

That's a good point on the CPU usage, I didn't think about it when I wrote that, thanks.

Memory does not appear to be the problem. CPU usage is an unreal 200 - 250%. I also found that the game keeps going just fine while in the background. I had it displaying on half my screen, while I tabbed to a program on the other half. The game never visibly stuttered or anything, but I couldn't tab back, it was unresponsive, yet still playing.

I never once experienced this issue before that patch, but I can't 100% guarantee that is where it started. I wasn't playing as much around that time. So perhaps I shouldn't have said that.