I use to feed my mixed flock unmedicated grower (18%) and free choice oyster shell. A few times a week I gave them fermented feed and sprouted grains. And once a month, a mix of: meat (raw and/or pinkie mice), eggs, herbs, vegetables and fruits, sometimes a tad of dairy. Also, live feeder insects! Silkworms, mealworms, wax worms, grub worma, crickets, locusts...
I’ll feed my next flock the same, fingers crossed I can start having chuckens again this year.