In case someone else encounters the following error on a Mac:
The application “Stillness1.1.1Mac” can’t be opened
This happens because the application doesn't have execution permissions. This is how I managed to fix it (I am on macOS Catalina):
1. Navigate to the folder where Stillness1.1.1Mac.app is
2. Right click on Stillness1.1.1Mac.app and select "New Terminal at Folder"
3. In the terminal window, paste the following command:
chmod +x Contents/MacOS/Stillness1.1.1Mac
It might be necessary to add sudo in front:
sudo chmod +x Contents/MacOS/Stillness1.1.1Mac
Hope this helps someone!