I can use Sydney Pro with License activated. But when I switch to Bistro it does not recognize this license and e.g. does not allow to customize footer.
Bistro is a child theme for the free version of Sydney. While it’s easy to turn it into a Sydney Pro child theme, I don’t recommend it as it is old and we cannot update it (because it’s a child theme).
We do have a restaurant demo for Sydney Pro which you can import if you’re using the latest version: https://demo.athemes.com/sp-restaurant