Sometimes my students double click on the compressed file and (on PC for example) this takes them to a misleading dialog that is a preview of what's in the zip file. You can't run Simbrain from there.
What you have to do is right click and then extract the contents of the file, then run from extracted folder.
I looked around and couldn't find many simple tutorials, but maybe this will do
https://www.youtube.com/watch?v=r9hpiyzOOTYI'm not sure if this is the problem you are running in to but it might be