In a report from 9toGoogle, it has been revealed that there are at least four apps that have been disabled from running at 90Hz. This includes WeChat, Pokemon GO, and oddly enough, Google Maps and Waze, both of which are owned by Google themselves. However, for at least two of the apps, there is a reason why.
With Pokemon GO, Niantic had previously capped the game’s refresh rate at 30Hz to prevent the app from draining too much battery. Some players have also found that when trying to throw curveballs, a higher refresh rate actually did them a disfavor. As for WeChat, it seems that this is due to performance issues and that forcing 90Hz on the app is not recommended (presumably an update to the app to optimize it should fix it).
As for Google Maps and Waze, it is unclear why they have been locked in at 60Hz. It is possible that similar to Pokemon GO, these apps are heavy on the battery and so locking it in at 60Hz makes sense. In any case, this is something that should be noted in case you’re trying to force the 90Hz refresh rate.