Okay, so! INCOMING LONG POST FOR ANYONE ELSE HAVING THIS ISSUE!
This DID help me. My issue *definitely* started after U30. I have multiple game captures, display captures, and window captures all in one scene. It's never been an issue. Ever. I never have more than three game captures going at once (Game Capture just tends to work best for certain programs that aren't games, but are .exe's, two of which I use for my pngtube avatar), and I'm never trying to capture more than one *actual* game at once. Only one actual game capture is ever active, the rest are "sleeping"/"hidden" haha
Anyway. So I thought looked around in here at similar posts, and saw someone said, somewhat unhelpfully even if it was well-intentioned, that when the red dot is stuck in the top left corner, OBS will expand the game capture when it receives data to load into the game capture. And since the dot was showing AFTER we had already selected a game input that was currently running, it should have been loading that data, right?
So I took your link there, plugged it into File Explorer, and I saw the files in there. And I see that two of them hadn't been updated in a couple of weeks (which I had to take a couple of weeks off, and when I came back, I updated OBS, and then promptly had this issue with game capture....) So I googled "graphics hook obs game capture" and this post and this comment SPECIFICALLY came up.
Bug Report Graphic Hook.dll <-- OBSProject link, fyi
And wouldn't you freaking know it. Closing EVERYTHING, then zipping those two files as a backup, then deleting the two files...Then REOPENING OBS....And they repopulated...And updated. I added a new Game Capture and bam. It worked. Everything works now. Even made an account here just to update everyone and let them all know. So good luck all! <3