Hello Dark Dimension, thank you for your reply,
I am going to try the Fullscreen button now.
About the small resolution, I rebuild the game in Unity to that resolution so it can "fit" on itch.io. I tried bigger ones of course, but the game window went off the screen bounds which is not ideal for the type of the game I uploaded - and it also has a "portrait" orientation. I'm not sure, i will play with that a little bit more and see.