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It seems to be the case that the new unity version is just incompatible with Win7. I looked at the pinned thread and one of the recent posts is someone with the same issue, dev said to try an earlier version through beta, and that works perfectly fine; 209.46 works, the very next version 210.2 does not. So the transition happened between those versions.

That was 28th of February this 2025, that's recent; I don't think undoing this unity version change is infeasible.
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I played on Win7 years ago, but I just reinstalled it and can't get it to work; I'm getting the same error message as some other unity game that apparently also dropped Win7 support.

"The application was unable to start correctly (0xc0000005). Click OK to close the application."

This happens immediately on running the .exe or the crash handler file; I tried to use event monitor to get an idea of what's happening but as far as I could tell there WAS no event going on, it was an instant rejection of the attempt to run.
Supposedly this is a memory issue, but I've run a bunch of suggested fixes, system file checker, memory diagnostic, updating video / audio drivers, disabling data execution prevention; with no success.

The dev of the other game said that he thinks the issue was that they updated to a newer version of Unity that simply doesn't support Win7 anymore. The store page of Qud says it supports Win7; have you verified that it still does? Does anyone run it in Win7 without issue?

If it doesn't support Win7 anymore then that's incredibly disappointing, the store page needs to be updated to reflect that, and while I doubt that it's realistic in the slightest I absolutely feel that you should undo this version change in order to undo the damage. I bought and played the game, and if an arbitrary update made the game unplayable that's kind of BS.

If this is actually just an issue with my system though I'd be very grateful for any help.