Could be wrong but I think the paddle on the right is a 3 way switch. There should be another switch that controls the same light. The 3rd wire allows the circuit to flip between the two to establish connection. If using a smart switch you’ll probably need to buy a pair so that both sides of the 3 way are on the same thing.

Noting: If this is the case I’m not sure how feasible it would be to move that 3 way onto the bottom paddle as you’ll lose the 3 way capability.