Could it have something to do with Mac recently dropping everything 32-bit? Assuming your game is 64-bit, the Itch.io app running on a 32-bit Mac system wouldn’t find a “compatible upload”.
This could also cause weird errors, if you force a 32-bit system to run a 64-bit system, which could potentially explain the last error?
Please keep in mind that I don’t keep track of Mac updates, so I’m not sure if “High Sierra” or “Catalina” fall in either category, this is just a guess which hopefully can lead to a better understanding of the situation.