Can you point me in the right direction?

I'm new to construct, have dabbled a bit in the past with some prototypes but now there is a plan for a small game. I am making a downhill skiing game where you evade obstacles like trees and i want the player to start moving down the slope automatically and only being able to move left and right, the downward motion is automatic.

I tried the bullet behaviour but that doesn't do what I have in mind. Would anyone be so kind to point me in the right direction.

I didn't think of that approach. In my mind the player would be moving. But moving the environment with the player only being able to go left / right is an interesting option.

Would that work the same as a scrolling background like in an endless space shooter? With sprites for the objects like trees?

Yes like this, better to give the illusion I think because no need to make a huge level that the player moves down. Keep the background very simple and it should all work well.