Just in general, one thing I don't understand about Dak is that his accuracy really goes up and down. He has some games where he is just hitting people right in the hands and others where he is waaaaay off quite regularly.
If you look at the play in question, I think his footwork is terrible there and he seems to be sensitive to the rush. Weeks ago, Jimmy Johnson said that you have to give Dak "a clean pocket". I think he might be on to something as to what causes Dak to have these stinkers.
Before someone starts going off on the offensive line as the problem, go watch Joe Burrow play. That guy has great pocket presence and is constantly shifting around while keeping his eyes downfield and maintaining good throwing mechanics from the feet up. That's simply not Dak. Dak frequently drifts INTO the pass rush.
What to do about it?
1. Get a good run game. We have known for years that Dak does well with play action. Most QB's do but it seems particularly strong with Dak.
2. Early in his career (pre-Kellen), Dak got a lot of quick reads and throws. He made a killing simply throwing 5 yard outs to Beasley. I think some of that should come back.
Overall, I think that Kellen and Dak was just a bad mix when playing against good defenses. Kellen didn't adjust and it put Dak in positions that he wasn't comfortable in. Against average or bad defenses, everything was good.