I played the demo and here are my thoughts.

The pixel art is charmingly retro but the game mechanics need some work.

The first pathway down all you need to do is stand at the edge of the screen and the baddie from the next screen down will bum rush you and kill you from outside the screen. It seems like half the time I try to go down that path to the next screen I am instantly greeted by the you died screen.

The player hitbox needs reducing since trying to move into 1 tile wide spaces is rather annoying with the player hitbox being exactly 1 tile space.

The enemies could stand to be slowed down a bit for better player reaction time and the starting health of the player is not full and one shot = death.

still this game does have potential.

This was made using Gamemaker Studio 2, as for a black screen on full screen switching the only times I encounter that is during fullscreen changes while paused in game and as far as I can tell so far this is a result of how gamemaker works, this still shows the player hud.

Or was this a result of using the menu option at the title screen?

And yes as you loop through the game the difficulty increases.