A couple of things.

What you feed and what you can control depends on how you keep your chickens.
If you free range then obviously your chickens are going to eat a lot of other things that may account for all, or differing proportions of their diet.
So, for chickens confined to a coop and run the recommendations for feed around 18% protein and 1% calcium will be fine but a source of calcium made available in a separate container is advisable for laying hens. In theory at least, if you have chicks, cockerels and non laying or infrequent laying hens, they wont eat the extra calcium.
If you free range, even if it’s only for a few hours a day this ideal feed concept falls apart.
I’ve found the easiest way to ensure the chickens here who free range get to eat a larger proportion of feed than forage is to feed them with a 20% protein, 1% calcium feed in the morning. I make a mash by adding enough water so the small particles get taken up and not just the bits they like.
I don’t leave feed down, everything else that ‘free ranges’, free loads on the commercial feed, rats and wild birds in particular.

I feed them again mid afternoon; same routine, I don’t leave the food down.
In the evening I put the commercial feed down for them again but I feed them their treat food at this time.
Treat food; it could be lots of things but chickens are omnivorous so I tend to give them a small quantity of fish or meat in the evenings. They probably don’t need it because they will have eaten bugs, worms etc when foraging during the day.
If your chickens are confined in a run, I think giving them some fish or meat just before roosting time will not only give them a better balanced diet but will also give you a way of encouraging your chickens to be by their coops at roost time and not trying to climb trees or reach the highest spots they can in the run if there are any.
Yes, it’s a bit of trouble, but not as much trouble as having chickens with nutrition problems.
So, the chickens here don’t get scratch and treat food is at least nutritious.
