Oh hi Marc,
You can fullscreen the game by pressing F4, but I always had some bugs on my end while doing so (apparently gdevelop throws a fit when I fullscreen on Debain 12)
Additionally, the interact key stays constant throughout the game and it is displayed in the controls tab under the pause screen. If you would like the first time controls screen, you can press Period (.) when the game is displaying the start screen.
Thank you for playing!