How do I detect whether the player is sitting on a certain chair?

I’m making a boat, and I need to detect whether to allow the player to control the boat by checking if the player is in the vehicleseat. I’ve tried searching it up but i don’t understand any of the options.

Do you actually care who the player is?

You could cheat and just read the VehicleSeat’s Throttle and Steer values directly (or ThrottleFloat/SteerFloat):

local seat = -- ... some VehicleSeat

    print("Seat throttle changed to: " .. seat.Throttle)

    print("Seat steer changed to: " .. seat.Steer)