The main change here is the inclusion of the Android May 2018 security patch from the April 2018 patch in 5.1.1. Apart from that, the update also includes a new version of the Gallery app, which adds an updated design and a new ‘Recently Deleted’ category that temporarily saves deleted photos and automatically deletes them after 30 days.
The update also brings fixes for an auto-rotation stability issue, Wi-Fi connection issue and microphone not working for some AKG earphones issue.
The update log also mentions the addition of double-tap to lock screen. This is, however not a new feature as it was added as part of the OnePlus Launcher update through Play Store and is also available on pre-OxygenOS 5.1.2 devices that got the launcher update.
The update is being rolled out and you should see a notification soon if it isn’t available already.
News credit : Gsmarena