itch.io

 Try these steps:

1. Move the application to your Applications folder.

2. Open Terminal.

3. Paste

sudo chmod +x /Applications/Mac.app/Contents/MacOS/TheRadiants

(note the file location may be different for each user, so confirm the file path before
pasting)

4. Press Return/Enter.

5. Enter your password when prompted and press Return again.

6. Open the Radiants application.

Did you right-click, open? Then you'll usually get a prompt that's like blah blah we don't know this developer, and you can choose to open anyway.