From my point of view, you don't have to put an "E" that big to say that you can interact with it. For the rest, the idea is good, the levels could be made as difficult as you want.
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Thanks for the feedback. It's the first time I made a game like this and in a future game I think I would change this completly by having the "interaction signal" based on the player (Screen Space) instead of on the object (World Space).
That probaply is also way easier to implement (It would only need one element).
I noticed that this is also what most other games with FPS camera do.