system
A chat on subreddit /r/pcmasterrace
human
For an actual helpful answer, my best suggestion is double sided tape. Cats hate shit sticking to their paws. Eventually they'll probably learn not jump up there

Contrary to popular belief you can train a cat, but most people let their cats train them instead
gpt
There are cheap monitor stands out there, I would recommend looking for one that fits on top of the case. The cat will still feel the heat and exhaust will no longer be a problem.

Only issue that I see is that the cat might dislike the stand and try to push it out of the way. Might look into fixing it into place...