in terms of gaming tropes, "Flappy Bird Clone" is about as overdone as it gets, but i do like the teleport mechanic. my issue with it is that you cannot control how long you will be invisible, so oftentimes you'll immediately hit a wall upon regaining control. likewise, the witch starts falling before their "exiting portal" animation even finishes, so all-in-all you'd likely just die when teleporting. i also don't like how the pipes were just retextured as towers as a way to fit the theme; feels a bit too much like an afterthought.
still, the assets and art look great! the fact that this is your first game and that you managed to put it out is nothing short of an accomplishment. great job! i hope you had fun, and learned a lot about development in Godot! (or in general)
consider trying my game as well!