Hello @MK13 & @CoffeeforClosers,
Unfortunately, webhooks from ArcGIS Online and ArcGIS Enterprise do not identify which field has been updated, only that the feature layer itself has been updated.
You might want to add it as an idea in the ArcGIS Online or Enterprise communities to provide more detail in the webhooks.
-sean
Sean McGinnis - ArcGIS for Microsoft 365 Product Manager