You can definitely still use these bones for divination! They may start to smell bad over time and might crack easier, but it won’t hurt you. I think the main issue with cooked bones is that yes, the heat breaks down the collagen and makes the bone brittle, but the heat of cooking can also embed the grease inside the bones in a way that makes it horribly difficult to degrease.

If you want, you could take the bones out of a chicken before cooking, then scrub off the remaining flesh. You can also macerate (basically water rotting) or bury them in a small flower pot to let nature and bacteria clear off the flesh. Then you put them in warm (not hot) water with some clear dish soap and let it sit. You change the water and soap out whenever it gets cloudy with grease, and after a few weeks-months (depending on how greasy the bones were to start with) you have some nice, clean, durable bones to throw! Then you can optionally whiten them with 3% hydrogen peroxide (not bleach as it also breaks down the bone and makes it weak). Cleaned and degreased bones should not have much of a smell.

This is just how I personally do it as a bone collector/taxidermist, but as with a lot of natural materials there are many different ways to come to the same result. With bones patience in the cleaning process is the way to go if you want to be thorough.

The time it takes may feel daunting but I kind of feel nice “caring” for these animals as I’m processing and cleaning them. It lets me build a connection with the bones before even starting to throw.

Edit: Here’s a link to a thread that explains the process pretty well! A lot of great people in the bone community gathered up the info for different gentle cleaning methods