This research paper suggests that electrolyte imbalance was not clinically significantly different between a group of runners that cramped and another group that didn’t. Serum electrolyte concentrations and hydration status are not associated with exercise associated muscle cramping (EAMC) in distance runners - PMC
While magnesium deficiency is known to cause muscle cramps, that does not mean that exercise related muscle cramps are due to lack of Mg necessarily.
For me, personally, cramps have become rare as I’ve paid more attention to my hydration and have been better at maintaining fitness even throughout winter.