When asking Oppo's smart assistant for the ColorOS 12 release, it would tell you that it's September 13 but in an official Weibo post, the company announced that the next version of its OS will arrive mid to late September.
This also means that Google will release the stable version of Android 12 very soon. Unfortunately, though, we don't have any more info about the supported devices and the list of new features and changes. We might have to wait a bit longer for those.
In the meantime, Oppo shared its collection of wallpapers, which is going to be released with ColorOS 12.