How do I create a path with a curve loop?

If you are willing to draw this path manually, you can use timelines.

dropbox.com/scl/fi/n8obqdjizvv58o4bn6i28/quadrifoliumpathexample.c3p

A quadrifolium is a polar equation, so you'll want to describe it in terms of rotations. Specifically, it has a sine curve with an angular frequency of 2, that is, for every full rotation, the sin cycle should complete twice. We happen to conveniently have both rotation and sine behaviors available to us.

To rotate it, change the starting angle.

PS: To adjust the duration of the cycle, you'll have to change the speed of the rotation and period of the sine wave proportionally. Rotation speed is in degrees per second, and sine period is seconds per cycle. Again, you want two sine periods per (360 degree) rotation cycle for a quadrifolium. So 360/rotatespeed will get you seconds per rotation cycle, and divide that by 2 for the desired sine period.