posting quickly but read it in drunken botanist how the bark was used in liquor bitters , and still is
(edit was going to get reference maybe later )
About seeds though
here is a recipe to roast seeds of rhamnus species
(hank Shaw is pretty good non the less)
https://honest-food.net/california-coffeeberry-edible/I have wanted to try this a number of years with our invasive European buckthorn (seeds )
I actually have some dried berries outside back door
(wanted to try to use for dye for cloths which I have been curious about,
but have never seen a written reference to use yet so just for experiments
The entire upper USA (midwest) seems to be invasive European buckthorn though Rhamnus cathartica )