Thanks for the info.
How are you running MasterPlan? Through itch?
EDIT: Also, do you get any error messages from the operating system, or does it simply not open?
Can you post the results of the "log.txt" file in the MasterPlan directory?
Viewing post in can't open MAC osx 10.15.6 (19G73)
Not sure what you mean by "jumped right off", but it sounds like the application isn't loading because the download isn't completing properly. That might be why you're being prompted that the downloaded zip file's corrupt - despite the fact that you can unzip it, the files within might be incomplete. I think it might be an issue with your internet or with itch's servers that aren't properly serving the download for you.
Try restarting your computer and router / modem, and then try downloading it again directly from the itch page in a web browser and seeing if it completes the download properly like that; if it doesn't, then try installing again through the itch app itself.
Forgot to reply to this; if this is the case, I'd imagine it's an issue with your internet or browser. Try a different browser, because the itch app (as far as I know) downloads apps from the same source as the browser (i.e. there's no difference in files when downloading through the itch app vs browser). Basically, I don't think I have any control over this particular behavior from my end.