A ball, a pyramid of pegs, and gravity
Plinko online is the least complicated game in any lobby and somehow one of the most watchable. A ball is released at the top of a triangular field of pegs. It falls, it hits a peg, it goes left or right, it hits another peg, and it keeps doing that until it drops out of the bottom into one of a row of multiplier buckets. That is the entire game. There is no timing, no skill shot, no decision to make once the ball is in flight.
What you actually choose is the shape of the board before you drop: how many rows of pegs it has, and which risk profile the buckets use. Everything after that is physics doing what physics does. Watching a casino plinko ball rattle its way down is a strange kind of pleasure precisely because you are a spectator to a decision you already made.