This ^^^ Rake it into a heap and let the chickens scratch around in it. Even better if you mix in some treats for them to find in there. None of my flocks could ever resist a heap or pile of whatever I was raking or sweeping up, however small. They LOVE scratching it apart.
If your flock is confined to a run, pile the leaves in there for them to scratch in.
I throw a thick layer of dry leaves in the run every fall. The run is covered and the chickens love to have a snow free area to scratch. I throw some seeds out, keeps them busy on days where they don’t want to go out in the yard. By spring time it’s all broken down