No there was never a rule about “telling the truth” the rule was “equal time”. So if one party said “vaccines keep people from dying” and the other party said “vaccines would cause you to grow extra limbs” you had to allow them both on.

Second, it had nothing to do with the Supreme Court. The theory was that the airwaves belong to the public and the FCC has jurisdiction. It never applied to cable channels like FoxNews

Third, the current FCC is going after broadcast networks for not being fair under the rule