You will probably notice that the first time you open the app, your OS will tells you this app is from an unknown developper.

The reason behind this message is that the app is not signed on none of the platforms because it cost money to do it.

On windows, the game will be restricted, which is not a problem since it require no restricted function, on macOS you will have to open the app a first time, get the message, then go to system settings > privacy and security and scroll down until you see the message that let you open the app.

Edit : the game might also be recognised as a virus by anti-viruses, the reason for this is basically the same as above : I did not pay for a certificate that is used both to sign the app and to be considered as secure by anti-viruses.