If you're genuinely curious, you can peruse any of several threads from a year or so ago that include posts about some of the big-name engineers who had signed on to mixing in Atmos, and about Dolby's overall strategy for working with Universal to equip more studios and train more mixers. (In the May 2020 issue of Mix magazine, a few of those engineers specifically discussed their mixing techniques for back-catalogue stuff.) More recently, people have posted lists of the dozens of studios--well over 100 at this point, I think--in the US and around the world equipped for Atmos, as well as promotional videos of engineers from some of those studios talking about their work.
I've been as skeptical as anyone of Dolby's hype and the streaming services' handling of Atmos. The vaunted 10,000 tracks have not yet materialized--I think the last tally I saw of what was available on Tidal was more like 2500 and counting (although that seems low to me), and too many of those are accounted for by contemporary pop and R&B that I don't care for; "hall ambience" remixes of classical material, new and old, on DG and associated labels; and underwhelming treatments of classic Blue Note albums. But in the past couple of weeks, it seems like the floodgates have finally begun to open. There's clearly a lot of newer stuff in the pipeline and probably more old stuff in holding tanks. As for the legacy tracks: many of them are ho-hum, but a few are truly impressive. A handful of newer releases are downright mind-blowing. Some mixers are more famous or more talented or more daring than others, many are still learning, and in any case Tidal has been inconsistent at best about including mixing credits in their metadata. But I don't see any reason to suspect a vast upmixing conspiracy, or to doubt that over the past two years, a couple hundred mixers would have been able to tackle 10,000 tracks between them.
