How can I run 2D game on my 3D scene and change playable character?

I need to make a 2D game in which the player can pave the path of the platform, but for some reason the input just disappears and I can’t control the 2D player, that is, move for him, and if I set him as the main player, everything works, even if I turn off the main player completely.

If someone knows or encountered a similar problem and solved it and writes in the comments, I will be very grateful.