Technical question:
If I add gelatin powder to my bone broth, am I breaking the fast?
Technical answer: yes.
Practical answer: not necessarily.

This is sort of a pet peeve of mine, I subscribe to a facebook page for a ketogenic diet, and people are always asking questions like this. Usually it's somebody who just wants to have one or two coffees or teas in the morning with a little bit of cream, and somebody will tell them an absolute no.

Take an empty cup. Put a single drop of water in it. Technically, it's no longer an empty cup. But neither is it a cup containing an amount of water that's useful for most purposes. Very small amounts of food will break a fast, that isn't to say necessarily that breaking the fast in this way will have much of a consequence--that the person's metabolism will be all that different from a fully fasted metabolism. Take an example, a person is eating one meal a day, at dinner. Now they change things, add 100 calories as heavy cream in the morning. Things aren't the same as if they'd just had water. Obviously they aren't the same as if they'd eaten half their day's food at breakfast--and I think they're probably closer to the fasted state than the fed.
Try a thought experiment, three "square meals." One person has 600 calories per meal, the other has 200. They are both certainly breaking their fast, three times a day. One ate enough calories to fill up their glycogen stores, so that as they approach successive meals, they will still be running largely on the glucose from the previous meals. The other person didn't eat enough to do this--so before getting to the next meal, they're already returning to a fat-based metabolism. Any amount of food will break a water fast. But I think a better question might be, "will x amount of food make enough of a difference to my metabolism, vs. what it would have been if I had not eaten at all, to remove the benefit?" I think a little bit of gelatin is unlikely to remove the benefit--and even if it reduced the benefit slightly, that might be outweighed if the gelatin made the fasting that much easier to do.