This took me way longer than it should have, sorry if my original answer misled you.
Using timelines and lerps for this sort of thing can be limiting, instead try to recreate this.
Basically,
if the player is not pressing any buttons then move the lean amount to 0.
If the player is holding left or right make a number go up or down.
If the player is holding two left and right at the same time then don’t do anything.
Plug LeanAmount into your rotation.
If this works for you then please mark my answer as correct by clicking the little tick icon beside the two arrows to the left.