I think it depends on the bitch in question. Puppies actually are started to be naturally weaned by the moms somewhere about 4 weeks if another food source is available for the pups. Teeh are coming in, it hurts! Some bitches will allow the pups to continue to nurse for longer some will be ready for it to be done. They are still around the pups and they still interact with them and there is so many other things the bitch is to the pups then a milk bar.
What we do is start introduing ground kibble or ground meat around 3.5 weeks and by the time the pups are 6 weeks they are usually weaned. At 6 weeks, we remove the puppies from the bitch at night and they are housed together in a pen. Mom visits the whole day. At 7 weeks they are individually crated and housetraining is started. We place puppies between 8-10 weeks and everyone is use to the crate and started on housetraining. Mom is around and some "aunts' to teach them manners. Ember is excellent at this.
Diva always liked her puppies. She would never wean them on her own and whenever they were around she would let them nurse. I had to physically remove her at 8 weeks and keep her away. But when they left she was like Thank you and never missed them. She played with them all the time. Whne they came back to visit, she was happy to play with them but no more so then any other dogsshe had known.
Vogue, who is Divas' niece would be done with them at 5 weeks. Snarly , stay away from me , no nursing at all she would play with them but she would have no part is silliness. She was always happy to see them go.
Even if we kept a pup longer to 12 weeks or more the moms would spend less and less time with them on their own after 10 weeks. Puppies start looking to each other and the older puppies after 10 weeks and IMO can overbond to littermates after 10 weeks. So if breeders keep them, they should be being seperated at regular times.
That is something I see all the time with litters that come into rescues. No socialization, no seperation- makes over co-dependent puppies. SO if a breeder is keeping a puppy to 10-12 weeks, they better darn well be starting socailization and handling with them and not just be letting them hang out together.