I'm joining the conversation in case there's anyone who's ending here in 2025 like me. I'd also like to know if there's a way to know the values ​​before the modified ones or simply the fields that have been updated. I do not make the connection through web hook, but directly with the Logic Apps connector for Azure DevOps. It seems that, using the web hook, you can specify the trigger more.

In my case I want to create a child item when it changes to a specific state. I don't need to know what the previous state was, but I do need to know if it's the state the field that has been modified. I've seen that I can solve it with the item's modification date and a specific field for the state modification date, but this doesn't exist for all fields. If it is useful for someone who is looking for a solution to the case presented here, I would try to deduce the previous state from the text of the "System_Reason" field, since this will indicate the reason for the state change and by default it mentions the previous state. It's not ideal but it might be useful. Or directly use the web hook method.