I have 2”-4” rocks as “mulch” all around my flower beds.
They do scratch in it but they don’t move it around much.
And my birds DO like raspberries so that may or may not be an option.
I had a large raspberry patch with thorns and they loved hanging out in the middle lol.
It’s gone now because it got dug up to make room for the walk-in coop.
My garden was created by the former owner of our house.
It’s very nice.
There are 26 rose bushes and each is surrounded by scalloped stone edging and my birds love dust bathing in the rose beds.
Doesn’t harm the roses at all.
Unfortunately they almost destroyed my hostas but I caged them to save them but they look terrible lol.
Also had to cage the Dusty Miller from being trampled and dug.
They left the daisies alone but ate half of my clematis even though it’s supposedly toxic to them.
Somebody didn’t tell the chickens.
They loved my asiatic lilies too.
And trampled the irises but didn’t eat them.
Trampled the day lilies too.

They’re not dead they just look like crap.
The bigger problem that’s already been mentioned is they dig and trample plants.
So anything newly planted or not yet established has to be fenced off or caged in some way until it’s big enough not to die from their “attentions”.

Look for hardy plants and shrubs with sturdy woody stems/branches and/or thick leathery leaves.
Amazingly most of my flowers have survived the chickens but I have a massive lawn they love to snack on so that helps.