Maze of Ith can target an untapped attacking creature. It will still prevent damage in that case.

The creature isn’t removed from combat; it just has its damage prevented. It’s still an attacking creature until the combat phase is complete.

You can activate Maze of Ith’s ability targeting an attacking creature you control during the combat damage step or the end of combat step. It’ll be untapped and the damage it had already dealt won’t be undone.