The update brings November 2020 security patch, improved call performance, and some general fixes and improvements. You can check for the update manually by heading to Settings -> System -> System update -> Check for update.
It’s worth mentioning that OnePlus has already released the Android 11 update to the global variant of the OnePlus 8 series smartphones. But, T-Mobile’s OnePlus 8 is still in the queue for the Android 11 update. [source]
