One has to dig into the novels for some of this, but Picard took his promotion to oversee the evacuation plans, so in theory, Starfleet already knows about the supernova and is beginning their initial evacuation effort.

The Utopia Planitia fleet was a major project, but evacuations took place even before the fleet was built - Elnor’s colony was an evacuee settlement, and Laris and Zhaban stuck with Picard after he rescued them.

I had been hoping that such a major re-evaluation of Starfleet’s mission would affect this show, but it was not to be.