OnePlus slightly postponed Android 11 to the 7 series. However, it seems that now they are starting to send open betas of Android 11-7 and 7 Pro.
So, OnePlus seems to allow some users to test and evaluate Android 11 for mobile in beta. The company will soon release a stable version of Android 11 with OxygenOS 11 interface.
You can read more about the news here.