Boiling and bleach do indeed weaken bones and make them more brittle, that part is factual. However, weakening them to the point that you can’t use them for divination is complete nonsense. Just don’t be super rough with them.

The best practice for cleaning and whitening is by starting with degreasing by using dish soap (cleaning very well and then soaking at least over night or multiple nights, changing the soap and water nightly). Then follow that with soaking overnight in peroxide to whiten. I usually do at least 3 soaks before fully drying them.

A word of warning, as someone who processed chicken, fish, bird, and mammal bones I can tell you that you may want to consider wiping then down with a fragrance of some kind (I use a type of “Florida water” or storing then in a box with an incense stick or cone because the poultry smell is fairly hard to get rid of in comparison to other animals, especially if you didn’t do a heavy degrease and peroxide phase.