On average, the D less R margin in the early vote mispredicted the final Clinton/Trump margin by 14 points! Pollsters get yelled at when their polls are off by even 3 points, and anything more than that is considered an absolute disaster. Imagine if a poll was off by 14 points: no one would ever listen to it again! And yet we get the same frankly amateurish analysis of the early vote in every election.
Not just COVID, Trump’s main strategy in 2020 was to turn “taking the pandemic seriously” into a partisan issue in order to make it so early and mail voting become disproportionately blue (there was no significant correlation in the past) while poisoning the well on those ballots’ legitimacy.