Starlink user terminal is "physically" not designed for working in motion. That is, it has not passed any safety tests that ensures it won't dismount, and fly off and damage property or injure people. The Starlink system is absolutely designed to work at high speeds (both as evident from comments in this post from people maintaining connection at 100km/h to it being deployed on airplanes).

From the horse's mouth: https://twitter.com/elonmusk/status/1529089543969943553