Hi Silverhawk! There should be an executable named SplodyDarwin64 that you can run. I don't actually have access to a Mac to test on, so not sure on exact steps. It's possible it lost the "executable" bit when getting packed for itch.io, so you might need to use the terminal and run:
chmod +x SplodyDarwin64
And then run ./SplodyDarwin64. If that works, let me know, I'll try to fix the itch.io build process and update the instructions.