In this context, Google is the third party. Plenty of apps use the Google Analytics SDK[1], or the newer GA Firebase SDK[2] for their analytics.
[1] https://developers.google.com/analytics/devguides/collection...
Of course they send your info to a “third-party,” that party being the advertiser(s).
The advertiser creates and advertisement and passes it to Google with a selector, "We want to show this advertisement to men over the age of 35 in Milwaukee" and a price/click.
When someone who fits the selector arrives, the advertisement enters into Google's auction.
If it wins the auction, it's rendered to the customer.
Google doesn't say "Here's the list of our customers, and who they are, let me know who you want to send ads to".
Google is a one way mirror. They will suck in as much data as you want to give them about people, but it's virtually impossible to pry any info out of Google that's at an individual and identifiable level. Only aggregated performance information is exposed to advertisers, and the ability to mix and match targeting criteria based off of those dimensions that they expose.
Even with their enterprise marketing products like DoubleClick you can't pry out individual-level data. DoubleClick customers used to be able to export an anonymous ID, so they could use independent third-parties to consolidate conversion and impression data and measure attribution across complex marketing campaigns. But even that isn't possible anymore, due to GDPR concerns[1].
The closest they now get to "sharing" user data is Ads Data Hub[2]. And by sharing, I mean they expect you to share all of your data from outside of Google, which Google will then connect to their data and allow you the privilege of running aggregated queries. But they actually keep their side of the data firewalled off, and it's not human readable or accessible at the row level, only in rollup queries.
In the ad world, I can assure you they are far more protective of user data than most anyone else. The size, effectiveness, and dominance of their marketing channels afford them the ability to take that position without it materially impacting advertiser spending. Very few advertisers take such active measures to insulate exposure of user data from advertisers. And for many that do invest resources in such endeavors, it doesn't mean that they don't provide user data to advertisers. It just means that they don't provide it for free anymore.
[1] https://adage.com/article/digital/google-s-move-remove-doubl...
Oh, don't worry, only the most data-hungry machine ever built has your data.
It's only mildly reassuring to me relative to how loose I know most providers are with leaking user data. And because, having interacted with it from the advertiser side, I can tell that they not only recognize the long term value in protecting user data, but that they also invest the resources to design their systems and processes with that fundamental premise in mind.
Conversely, I also recognize just how much they do know about me, and just how privileged of a position they're able to take due to their market-dictating scale. The thought of their growth ever stalling terrifies me, since it can give them cause to re-evaluate that fundamental premise if they ever need to shore up their numbers.
That being said I think this is a good compromise and I hope Apple applies this to all vendors.
I think the biggest winner here if I read this correctly is AWS and other cloud providers. The most straightforward way for someone like mouseflow to comply is to separate each customer to its own instance in a way that mouseflow has no access to user data.