This is a terrible argument. It's a play on the logical fallacy of the false dilemma. We have to either focus on what got us in there or focus on the fiasco of the withdrawal. It's not a binary choice. We are more than capable of acknowledging the failure that was nation building in Afghanistan while also acknowledging the failure that was the withdrawal.
This argument is the last refuge of someone who doesn't want to confront the fact that a politician they support screwed up. There's no defense of how the withdrawal is playing out. There's plenty of blame to go around but the Biden administration definitely screwed up and that should be addressed. I've actually been impressed with the number of Democrats who have publicly criticized the President's handling of the withdrawal. I don't think there would have been as many Republicans criticizing Trump had this happened on his watch (and I think it would have played out the same with Trump).
Biden fumbled the ball on this one. There's no doubt about that. He needs to wear it and stop trying to refocus attention on the decision to withdraw being correct and stop trying to deflect the blame. It's a weak look. Wear it, say we're going to do everything in our nation's considerable power to evacuate people safely, and say you won't make the same mistake again.