Not directly programming or coding GUI from scratch with a library or something: Have you considered using a game engine like Godot ( https://godotengine.org/ ) ?

You would have a toolbox for several essential GUI-elements. You could visually create the GUI and add functionality by script. Also, there are several possibilities to handle different screen sizes and touch.

You would have to learn the UI and concepts of Godot but the documentation is ok and there are plenty of tutorials available.

Sniper Elite 4/5 has a 2 player coop for the campaign

sorry, should have clarified it more: In Sniper Elite 4/5 you can play the campaign in 2 player coop. I have not played The Saboteur so I don’t know about that one…

the campaign is really cool in coop btw.

Edit: I mean the campaign in Sniper Elite 4/5

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