The first thing that should be done is making your collision more reliable. This can probably be achieved by starting with simple shapes and consistent sprite sizes. Also, it'd be more fitting if the ground and blue enemies were custom assets like the character and flies. This won't garuntee that it'll be good, but it will clearly indicate that care was put into it.
I used GDevelop once, so I understand how much of a pain it can be to do things.