The best way to install and run FlowScape is to use the itch.io app
There are a few advantages of using this, it lets you manage multiple installs, resumes downloads if you lose connection, sets permissions on MacOs, and has an option to check for updates and only install what is new, usually a few megabytes.
If you are still having trouble, you can Re-install
There are a few other things you can try.
If you are stuck at the loading screen, give it a bit of time, its loading a lot of textures.
Clicking on the screen while loading, could cause it to crash.
A program called Citrix has been known to cause trouble with Unity based apps. Check that you don't have it installed, and disable it if you do.
On some Macs you can try windowed mode instead of fullscreen
Hopefully this will fix any issues you are having
If you need further help or would like to ask for a refund, you can contact me on discord, my username is Pixel Forest#4545