The source – support.google.com
Due to the cancellation of third-party cookies, the introduction of ATT and other changes, data showing the user's purchase path has become unavailable. Modeling conversions will help restore it.
Google uses machine learning to look for trends between conversions that were observed directly and those that were not. Example: If conversions made in one browser are similar to unattributed conversions in another browser, then the machine learning model will predict overall attribution.
Modeled conversions are available in Event, Conversion, and Attribution reports. In addition, in studies in which the advertiser sets parameters related to events.