IMO food/treats aren't great enrichment items. For short term use yes a flock block or extra treats are great to draw their attention temporarily but it can dilute down the protein in their diet which may be a contributor to picking.We have a variety of breeds—an Australorp, Orpington, Wyandottes, and Brahmas. We hang a head of cabbage for them to pick at, as well as give them flock block and several roosting bars. I can get pictures of our setup later today.
Food also isn't something they can really interact with other than eating. Can't climb on it, hide behind it, sit on it. Do they use the roosting bars you have set up? Do they have a dust bath available? If you have garden trimmings, pulled weeds or dried leaves, have you tried piling those up in the run? Chickens love digging.