In my experience, raw and unhomogenized milk can be shaken and the cream mixes with the milk. Pasteurized unhomogenized milk separates and doesn’t re-mix. If you buy whole milk that way (Stauss Organic) it’s basically skim milk with a chunk of hard milk fat at the top, unless you warm it, then it turns to grease floating on top that no amount of whisking will incorporate. Why do people want this?

Just accept that modernity has given you safe, non-chunky milk. It’s a good thing.