It may not be the best move since the engine proposed something diffrent after longer thought. But why is it even good? Isn't this just a wasted tempo?
Stockfish and RubiChess agree that Qb3 is the best move. RubiChess (blue arrows) is only considering attacking while Stockfish (green arrows) has Kh2 and Kh1 in its top moves (+6.25 and +6.99 versus +6.57 for Qb3).
I think the general idea is that the black rook on e8 implies the strategy to get that rook to e1. The move Kh2 avoids that check.
I don't really find that argument convincing myself. White is clearly ahead so just increase the pressure and black will probably have no time for a counterattack anyways.