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.