How to test the game on the site?

Question

Software testing

We were given the task to test the layout of the game. I am a beginner tester. The game on a separate site is 25 minutes long. The question is how to determine on what number of browsers it needs to be tested, on what number of mobile devices, and the number of browser types. And it is necessary to go through it completely in all emulators, if the layout in all tours is the same (the beginning is different, everything is the same in the tours, and the last splash screen)? Testing will take place in the browserstack. Manual testing is expected.