My opinion on this is that chicks (or grown chickens) do not NEED herbs or any other treat. As long as you are feeding them an age-appropriate chicken feed it contains all that they need. If you feed them much of anything else it can affect the balanced diet of all nutrition in their chicken feed. I consider giving them chick-sized grit at a very young age a good idea in case they eat something that needs to be ground up. But if all they get is chick feed in mash or crumble form (even pellets when they get older) that has already been ground up so they do not need grit.
Some people have the urge to give their chicks and chickens treats. Some people seem to need to do this whether the chickens need it or not. As long as they have grit to grind it up and that extra is a relatively small amount of their diet (not enough to cause unbalance in the balanced nutrients they get from the feed) I don't see a problem. Mine forage for a lot of their food. I give them table scraps and garden wastes. Not to enhance their diets with specific extra nutrients they really don't need but to reduce my feed costs. It also gives me pleasure to see them living somewhat naturally.
One of the first things my broody hens do when they bring their chicks off of the nest is take them to a place they can peck at the ground to get grit. Then she takes them out foraging. They get bits of vegetative matter by pecking at the ground, eat some growing greens, and an occasional creepy crawly. If some of those growing greens happen to be herbs so be it. That will not poison them or harm them as long as it is a small part of what they eat overall.
The only treats I give my brooder raised chicks is a little dirt from the run. This gets them grit, lets them start working on flock immunities they will need, and gets them probiotics from the adults. On rare occasions I may drop a bug of some kind in there if I happen to catch one just to watch them play keep-away with it.
In my opinion, if you want to feed them treats it will not hurt them as long as the amounts are fairly small. But people that feed them treats to enhance their lives probably need to do that a lot more than the chicks need to receive it. Nothing wrong with that. You are enjoying the experience and not hurting them.