"The extension of his left arm from elbow to wrist to push off his defender is illegal, and it is an offensive foul. An offensive player may not push off their legal defender in any way.”
Note that they emphasized "the extension of the left arm from elbow to wrist". They could have phrased it, "The use of his left arm to push off his defender is illegal." But they inserted the "extesnion from elbow to wrist" part and I think that's what the refs are looking for - a push off where the arm ends up straight.
Players have been clubbing the defender with their forearms, keeping their elbows at a 90 degree angle, but not extending so the arm is straight and the refs are allowing it. Tatum was clubbing Garland in the chest but as long as he did not straighten his arm like Jokic did in the video the refs let it go.
What I don't understand is the last sentence says, "The offensive player may not push off their legal defender in any way." That seems to say that even a bent arm pushoff is illegal, but the refs allow it. It also implies that throwing a shoulder into the chest of a stationary defender is illegal, since that is an armless push off, but that is OK as well.
I think the rule should be rewritten so that any off arm push off, even with the arm bent, is an offensive foul. It would make the game more attractive. There's nothing aesthetically pleasing about seeing the player with the ball battering his man backward foot by foot, clubbing him in the chest with his forearm over and over.