Did you try it without the itchio app already and download the zip file directly from itch.io?
There are a lot of possible reasons why the uninstall.exe might be missing. Windows could be responsible for some missing files. I did check it on my old laptop and was able to install and uninstall the game without any problems. You can try reinstalling the game to the same folder and see if the Uninstall.exe is still missing.
Hey! Your antivirus software should allow you to restore files from quarantine and flag them as safe to use. Antivirus Software will often falsely flag games made in known engines for different reasons. :) This goes for the Defender on Windows-Systems too.That should allow you to actually play and/or uninstall the game as needed. Should you not know how to handle that, you might need to look up a guide for your specific antivirus solution. Keep in mind that this is a free game for you to enjoy and the devs are actually pretty awesome for trying to help out in case of problems like this instead of just leaving you to your vices.