[Edit: asdfex pointed out in a comment that they do have two motor systems and the two sets of blades therefore are not geared together. So it's possible that they do do tricks with speeding up & slowing down the blades, and my argument that two motor systems are risky and heavy is clearly not correct. I'm leaving the rest of this here as I still believe that they use fairly conventional helicopter control systems (and certainly they use varying pitch), although clearly it's more complex than I thought.]
It's important to realise that Ingenuity is a helicopter: it's tempting to think of it as being a bit like the kind of multirotor drones we all know about, but it's not, at all.
With a helicopter with counter-rotating blades like Ingenuity you could indeed turn by varying the speed of the blades independently of each other and relying on angular momentum conservation. (A helicopter without counter-rotating blades do that because if it speeds up and slows down the rotational speed of the blades it also gains or loses lift. It could probably turn by controlling the rotational speed of the tail rotor I suppose.)
But using this technique to turn is absolutely horrible. It's horrible because it means that you need to be able to chose the rotational speed of the blades independently of each other. You can't do this with gearing from a single motor, so you need two complete motor systems to do this. That's both mass and really nasty failure modes: if anything happens which causes one motor to slow down you have a catastrophic accident rather than descending to the ground in a controlled way. You don't want even the possibility that the two rotors can rotate at different speeds.
And it's also horrible for another reason: as I said at the top, Ingenuity is a helicopter, and helicopters, to be useful, must have pitch control of their blades. Without it all you can do is go up and down, turn (at horrible cost in mass and safety) and ... let the wind blow you where it will. That's a very expensive, very noisy balloon (well, balloons can't turn).
So, in order to be able to move about with a helicopter, you need to vary the pitch of the blades both 'collectively' (increasing or decreasing the pitch by some constant amount) and 'cyclically' (varying the pitch depending on the angle of the blades. The first of these lets you control the overall lift, and the second lets you move around. Ingenuity does both.