Would it be expected that seeds from a grocery-store butternut (or acorn) squash would produce proper butternut (acorn) squash if planted?
It all depends upon what the squash was planted near while it was growing. The seed could’ve crossed with another squash, so you may get a hybrid of something.
Also, hybrid seeds (most seeds are hybrids, unless they specify they are ‘Heirloom’ or ‘open pollinated’) will give you SOMETHING, but it’ll be a throwback to the male or female used to make that cross in the first place.
So, if you’re willing to not care what you end up with, as long as it’s an edible squash of some kind, go for it!
I once had a zucchini cross with a winter squash. I ended up with a zucchini that was as long as a baseball bat and twice as hard, LOL! I think that thing sat in the corner of the kitchen for a year or more - and never rotted.