One-legged pedaling is a powerful technique to smooth out your pedal stroke and increase overall cycling efficiency. It forces you to engage through the entire pedal rotation, not just the downstroke.
Start on a flat road or on an indoor trainer. Unclip one foot and rest it on the frame or trainer. Begin pedaling with your clipped-in leg at a moderate cadence. Focus on making smooth, complete circles rather than just stomping down.
Pay attention to the upstroke and the transition over the top of the pedal stroke. You’ll likely notice some choppiness or dead spots in your rotation. Work on actively pulling up and over to create a more fluid motion.
Pedal with one leg for 30 seconds, then switch to the other leg. As you improve, increase the duration to 60 seconds per leg. Aim for 5-10 repetitions per leg during your ride.
Between sets, pedal normally with both legs. After a few sessions of this, you should feel a noticeable difference in your pedal stroke smoothness.
I think this advice might be out of date.
For greatest efficiency, I think modern pedaling mechanics refers to TDC-150 deg as the power phase, and some of the back side of the pedal stroke (240-TDC) are even (no or slightly) negative power.
First Google reference:
https://www.bicycling.com/training/a20021262/pedaling-mechanics/