Fix for slow OnePlus 6 after upgrading to Android 11 (Oxygen OS 11.1.2.2)

If you're reading this your phone has started to chugg hard.

The fix for me was to go to Settings -> System -> Ram Boost
Disable it. Whatever it is, it aggressively attacks the performance of apps and causes the slow down and lagginess you're likely experiencing.

One whole day on and things are looking fine for me.