Sorry for getting back to you a little bit late. The notifications on itch.io don't always come through for posts. Also, I'm sorry that you ran into this problem where it is unable to find the game. I've had issues with it before and thought I previously fixed it.
Here are a few solutions I found (not sure if they work) for a variety of Mac related issues just in case (and also for other people to see).
No Mountable File Systems:
Try running the following command in terminal. It simply allows apps downloaded from everywhere. Please tell me if you still have needed to use this command, since I have attempted to code sign most of the versions.
sudo spctl --master-disable
Unable to find game:
This could be due to a few reasons. Firstly, if your MacOS is too old or outdated, consider updating your software. I am confident that it runs on High Sierra (10.14), but cannot yet confirm anything before this. I think there might have been a previous issue where the macOS was out of date and created this error.
Another reason might be your browser choice. Try downloading the file from a different browser.
If all else fails, then try using this mirror link from dropbox: Mirror Link Mac. This is the link to v3.02 and will most likely be removed once a new version comes out (at which point I hope this problem has been resolved).
On a smaller note I read somewhere that moving the file to your desktop might help, but I read it in an older thread, so it might not help anymore.
I would love to know the outcome of this issue, since this is not the first time I have encountered it and have tried to ix this before. You can always join the Discord server if you need more help. You can also DM me from discord at anytime and I will get back to you as soon as I can.
Hope one of these solutions help!