the whole Nightshade thing is centuries old ignorance.I would recommend tomatoes but I‘m not sure you are supposed to give chickens nightshades (tomatoes, peppers, potatoes). Our hens love anything with seeds (melon seeds, tomato seeds, bird seed). Rice also, I scatter it around and they will dig up their bedding to find every grain!
Tomato leaves, in a diet solely of tomato leaves, is a problem. Give the birds a proper diet, and they will largely ignore the leaves. The fruit are just fine.
The outer bit of an UNRIPE potato skin - again a potential problem - but unless you are feeding your birds a diet of unripe potatoes...
and they will absolutely detroy pepper (fruits) of all kinds, while almost entirely avoiding the leaves.
If, otoh, you give your birds a diet of primarily "bad things", such that they must eat the bad things or starve, well... "Bad things" will happen.
The dosage, as they say, is the poison.