What's hilarious about Tatum's awful scoring half is that he's actually still having the most positive impact for the Celtics with a +11 to lead the team when we're -2 on the game. While not scoring, his gravity and playmaking is really helping setting up others to get good looks with 5 assists already.
But, yeah, time for him to start scoring and looking for shots beyond stepback threes. If they continue to collapse hard on you when penetrating, then just hit the open man.