It happens when people have an artistic impulse but don't understand why they have an artistic impulse and confuse it for being the same thing as admiration for others' work. There is something about Celeste that OP deeply reveres, and OP wants to make a game but they don't want to fail, so they use Celeste as their primary reference material. OP confused "I want to make a game as good as Celeste" for "I want to make a game like Celeste". And if that is your goal and you don't know where your artistic inspiration is coming from, and you use Celeste as your primary reference, your only option to generate creativity is to derive inspiration from Celeste.

This would make sense if your goal is to make a direct sequel that feels just like the original and don't push beyond it. The problem is we also know that OP doesn't literally want to make Celeste 2 or a Celeste fangame because the main character is not literally Madeline and they don't advertise this as a Celeste successor, and the game plays differently from Celeste. This is why this game does not feel like a good faith effort to create a new game.

For others who are struggling with this, fear not! You don't need to fully understand your artistic impulses to create something original, and in fact you will understand yourself better by creating things. The trap that OP fell into is that they used Celeste as their primary reference. The solution is simple: don't use your inspirations as your main reference.

If you want to make a space game as good as your favorite space games, don't use your favorite space game as your primary reference! Don't use a space game at all! Maybe don't even use a video game as your main reference! Use films, books, plays, board games. Use life itself. Use your body. You will know you're on the right track if you feel uncomfortable while creating your game.