If you were standing on a moving platform, like a boat, would it take more, less or the same amount of force to...?

Discounting things like air resistance, there is no difference. Why? Because the deck of the ship is not moving relative to you. And when you walk your force is only relative to the non-moving deck. So you can go either direction.

Remember velocity and force are vectors; so they must be specified relative to some designated static reference frame. In your case, that frame is the deck of the ship. And it's not moving relative to you.

You can test that by not walking. Is the deck moving under you (other than pitching and rolling)...no. So it's the static reference frame here. And the velocity and force are the same no matter which direction you go on that deck.

Of course were you on the weather deck and in real life, you'd be walking into the relative wind when going forward and walking with the relative wind when going abaft. So it'd take more force to walk forward in real life and on the weather decks.

If the boat is moving at constant speed, then it takes the same force and energy.

it would take the same