Like the Xiaomi 12S Ultra, the Xiaomi 12S Pro shows a discrepancy between the advertised manufacturer specifications and our brightness measurements. However, this not only goes for Xiaomi smartphones, but we also observed the same problem in the OnePlus or Oppo smartphones, for example. https://www.notebookcheck.net/Do-smartphone-manufacturers-often-cheat-in-their-advertising-of-display-brightness.648995.0.html
They do "cheat" in the advertisement of resolution, with Diamond PenTile RG/BG still being overwhelmingly common in smartphone OLEDs.
It also doesn't help when Notebookcheck reviews such as the one linked here forward the resolution specification number at face value, and post 22.5-degree-rotated matrix photos that obscure the issue.
Regarding brightness on these OLEDs, I'm much more concerned about what the highest brightness is that I can use on a regular basis without causing early burn-in. Though I do agree it's a bit sketchy to advertise a level that can't be achieved through any normal means.