A simple flappy bird clone - I would've really liked to see you expand somewhat on the idea or incorporate the limitation into it.
I'm not familiar with Gdevelop, but in Unity and some other engines you gotta make sure to enable "Filter: Point" and "Compression: None" on your pixel art textures if you scale them up - otherwise they end up pretty blurry, like in your game.
Regarding the games physics, it seems you have implemented some sort of "velocity" (i.e. player.position.y -= 10 per frame or something similar), but if you want to make it feel more like a force, you really need acceleration.
e.g. via something akin to the Euler method:
player.acceleration = input ? 10 : -10;
player.velocity += player.acceleration * dt;
player.position += player.velocity * dt + player.acceleration * dt;