The browser runs on 64-bit Windows 10 and above, as well as macOS (tested on High Sierra, Catalina and Big Sur).
In the folder where Undetectable was installed, right-click on the "Undetectable.exe" file. Select "Properties". In the file properties, on the "General" tab, check the "Unblock" option and click "Ok". Restart the program again.
By clicking on the "More" button, an additional button will appear in the window, which will still allow you to launch the installer.
Go to "System Preferences". Then navigate to the "Security & Privacy" section. Click on "Open Anyway" on the "General" tab in order to open or install the application. Another warning message will appear. Click on "Open". The application will be saved as an exception to your security settings, and you will be able to open it by double-clicking it, just like any other authorized application.