ALTERNATE FIX FOR MAC USERS:
After trying every suggestion on here and the discord page, i finally figured it out. You might have to get an app that converts the file before using the terminal codes! Using the Terminal codes and downloading Winrar alone didn't do shit, so I downloaded "The Unarchiver" app in the App Store (converts the ".7z" file so it's not a document file), opened the app, opened SU218 (so Unarchiver could convert it) and followed with these instructions:
"Launch Terminal [Applications/Utilities], then type or copy/paste chmod +x [including a space after the x]
Then drag the app you need to change the perms straight onto the Terminal window, which will fill in the correct path
Hit backspace once, as the last task will add an unnecessary space
Then you need to add the sub-path to the actual executable inside the app, so copy this & paste it onto the end of your current Terminal line: /Contents/MacOS/
Hit Enter
If that doesn't work, try the following: chmod a+x and chmod -R +x "
and it finally worked. The "chmod -R +x " variant is what worked for me personally. Idk why everyone is advising a 3rd party app like Winrar over app store archivers. Unarchiver was both way easier and faster to figure out/use.
The overall command in terminal should then look like this before you enter:
chmod -R +x /Users/Yourusernamehere/Downloads/SU_2.1.8mac.app/Contents/MacOS/
Hope this helps anyone still stuck
