IMO, it is an easy defensive schedule plus running.
I'd say 2019 or 2020 is when Dak reached his current form. That's when he really started erasing a lot of his bad rookie habits - remember when he'd spin out left and just chuck it? - but he also started to pick up some injuries that sapped his LB-ish athleticism. Couple those injuries with a big contract, and Jerry and friends coached him to stay inside the pocket and avoid taking hits.
The thing is, Dak is not really a pocket QB. He is smart enough and accurate enough to play it decently, but he's not the kind of Joe Burrow, Peyton Manning type super-processor who's throwing to his third read before your pass rushers even sniff him. Take away Dak's first read, get in his face with pressure, and he'll make a negative play. He's not good enough to punish a well-executed defensive play without ever leaving the tackle box.
Now he's starting to run more, and that stresses defenses a TON. It buys time, it changes windows, and it forces defenders to choose between playing the run and coverage. That's giving Dak some openings he can exploit, whereas say last year, he'd just throw the ball away.
Running is just a big part of his game, and we freed it up again post-49ers.