Just realized and got a new idea you can do BlackShibe box approach for this and found another post asking the same question.
Store the “unlocked sway” in a local vector 2 value. Since this offset is constant even if you stop rotating the mousr.
Add the mouse delta to the local variable multiplied by some factor for sensitivity adjustment.
Apply it using angles (see below)
Clamp the Vector2 X and Y values to prevent over rotation