OnePlus has issued Android 11 Open Beta 11 to the OnePlus 6 and OnePlus 6T. Android 11 and OxygenOS 11 will be the final OS updates for the pair.
https://www.notebookcheck.net/The-OnePlus-6-and-OnePlus-6T-can-finally-be-upgraded-to-Android-11.549926.0.html