I had the same problem, this worked for me:Go to settings>Privacy & Security>Full Disk Access, then click + and add Terminal (found in Utilities). Next open the terminal and run the following: sudo xattr -rd com.apple.quarantine ~/path/to/the/app.app , ie if the app is in the downloads folder use: sudo xattr -rd com.apple.quarantine ~/Downloads/RM_v3_9bMac.app, then input your user password, and then you should be able to open the app.