IMO the burden should be on Google to prove that they don't. The flow of personal data through their systems is opaque and they have plenty of incentives to monetize the data.
did you even read the article you linked
The usual methods for achieving this are government regulation and oversight (free of capture), and independent third-party audits (likewise).
The good news is that there seems to be ... some, slight ... progress in this direction.
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On the other hand, what Apple does with your photos that you allow to be exfiltrated through iCloud... that's your own stupid fault.