I didn't see the testimony, but I did read her book.
When most people think "targeted advertising", I think they are thinking about something like: this user is a middle-class woman between 18 and 25 who enjoys bicycles, so we'll show her ad X.
According to Wynn-Williams, Facebook/Meta is doing things like detecting when a user uploads, then immediately removes a photo--detecting that as a moment of emotional vulnerability (that is, the user was feeling self-conscious about their appearance), then bombarding them with ads in that moment for beauty products.
I think the former is 'obvious' to most people, but the latter probably isn't--probably because Meta and other advertising companies have put a lot of effort in to keep this on the down low--which is why Wynn-Williams is speaking about it publically.
(not accusing you of defending them BTW, just my 2¢ that this goes beyond what most people would consider obvious, imo)
For what it's worth, the judge also said that if the DoJ declines to prosecute, he will appoint another attorney to do so.