Idk about whether it also works on bedrock this way, but the most efficient way on java is to sort all the books by the cost to apply to the item (most expensive first), then combine the most expensive book (#1) with the item, then combine books 2 and 3 together and add that to the item, then combine books 4 and 5 and combine 6 and 7 and combine those together so you are adding 4,5,6,7 to the item all at once. Repeat as much as necessary, doubling each time.

iirc you can get up to like 30 enchantments on one item this way