Greatly depends on the climate, the labor willing to work it, the equipment you are willing to buy/maintain, and the inputs you are willing to import.
I’ve got just shy of 6. Plenty enough to keep me busy. We might grow 25-40% of our food for 4. I used to think I might buy a few acres from the neighbors but those days are over. Right now I am trying to figure out how to keep things running when the kids move out.
I like to think about what one person can maintain with minimal equipment and inputs. Ball parking, maybe 1/2 an acre of garden, maybe 2-3 acres of orchard, and maybe 100+ of pasture.