AM radio broadcast uses amplitude modulation, where changes in the carrier wave’s amplitude carry the signal. FM radio broadcast, invented by Edwin Howard Armstrong, uses frequency modulation, where changes in the frequency of the carrier wave carry the signal. Armstrong’s prediction that FM would be less affected by noise was proven correct, as noise tends to be unwanted amplitude modulation rather than frequency modulation. FM radio was able to achieve noise reduction levels previously thought impossible by AM radio standards. The discovery of noise reduction in FM receivers was surprising and contrary to AM systems, where noise elimination also partially eliminated the message.
https://www.johndcook.com/blog/2024/10/13/why-does-fm-sound-better-than-am/