Having worked at Apple, I will say I firmly believe they do not sell data. I worked in data science and we had the shittiest inference because we had essentially no access, even internally, to longitudinal or cross-app user data. Best we had was 15 minute rotating sessions for a single app. There are internal teams dedicated to deanonymizing data to try to narrow down users - if they can successfully do so, and relevant fields that lead to deanonymization get permanently purged from internal logging.

I can’t speak to the current architecture but Apple has shown a consistent willingness to sacrifice access to user data in the name of selling privacy instead at a premium price (you could argue precisely because no one of their competition have any meaningful posture on this). I do believe they are quite serious in their commitment to that, as they have found this strategy to be more valuable than the data itself.

Apple's incentives don't align to sell private data as their whole thing is privacy. They do that they tank their business. If you have proof that they are doing it -- I'd love to see it. (*3rd party actors from an app re-selling data doesn't count)

Google is 100% doing that because thats their entire incentive for the business. They sell low cost software / subsidized hardware on the grounds that you pay with your sharing data. That's the implied cost.

Show me the incentives - I will show you the outcomes.

Apple/Google make less money if they sell the data because their ad product would no longer have an advantage. So no, I don't think they do that.