I would actually like to see a source for this claim. Google did state that it would stop scanning emails for targeting ads "later this year" at some point in time. But I haven't seen a document after that reaffirming that this has been done.
I suspect GDPR would have been sufficient threat since not all people involved in a scanned email were guaranteed to be Gmail users, so gaining consent would have been problematic.
I'm not really sure this is 100% true. I recently got a fight confirmation email and immediately started getting "things to see in LOCATION" push notifications from Google maps. I'm not sure of course that they really read my email, but it did convince me to look at alternatives.