It can it also can go to h8, but both those positions are evaluated worse than taking back by king.

If Kg8 the king will get checked with tempo and white can now take with their dad pawn instead of being taken.

If Kg7 it could take the pawn back after rook takes rook but it would be in same position as sacrifice but again with a lost tempii.

So taking is the Kings best option and it does result in the same position and tempo as initiating the queen exchange first.

The slight difference at depth 20 on the eval for the equivalent positions is likely due to the fact that if they make any other Move besides taking queen back it would result in an even better position as if king went g7 or g8 after the check.

At least that’s what I assume, I could be off.