This is because the Apple Gatekeeper software doesn’t recognize the app as being signed or notarized by a trusted developer. There is a way to bypass this using the terminal, using the command
xattr -d com.apple.quarantine
Before hitting enter, you need to drag and drop the app from the desktop into the terminal at the end of the command.
This just overrides the GateKeeper software, and marks the game as “Safe”.
For instance, the complete command should look something like this after dragging and dropping the file into the terminal;
xattr -d com.apple.quarantine /Users/name/Desktop/DiBS.app