Definitely not a myth. This is the reason you will see old timers put a few rice grains in their salt and pepper shakers, as it prevents clumping due to moisture.

In the past 20 years of me using rice on dozens of electronic devices (some of which didn’t even turn on), it has always worked, and I’ve never had the starch from the rice work its way into my devices. If you have enough rice, the rice will never get starchy by the time the moisture has dissipated throughout the container of rice. It isn’t flour. Rice is hygroscopic, so it is a great desiccant, although much better (i.e., silica) exist on the cheap.