I would be very surprised if that were true.

In fact, I think I’d wager good money that there certainly are magnets strong enough that, when sized to fit the area of a typical cycling pedal, could resist any amount of pull force a rider might generate.

For example, here are 1.25” diameter round magnets with up to 95lbs pull force available on Amazon. A magnet on the shoe working with a magnet on the pedal would be expected to have even higher pull force. I would be very surprised if anyone was pulling their foot off the pedal with anywhere near that kind of force.

I’d further wager that the major obstacle in magnetic pedal/shoe attachment is not generating sufficient retaining force, but rather how to overcome such sufficent retaining force to make rleasing easy, natural, and safe.