"...the thin wires carrying power can crack over time, specifically after hundreds or thousands of swivels of the earcups (since they turn 90 degrees to fit flat into their case). That microscopic crack can cause issues with the connection.

By freezing the AirPods, the cold can cause the lining around the wires to contract, temporarily bringing the cracked sections together."

https://www.cnet.com/tech/mobile/airpods-max-freezer-fix/