How to Add Dual Window Support to Any App Without Root

Dual Window is LG's version of multi-window. By default, only certain apps that have implemented a specific flag in the AndroidManifest.xml file support Dual Window. If you're unrooted and looking to add Dual Window support to an unsupported app, you can follow this guide by a redditor to manually add support. Ideally, you can ask the developer behind your favorite app to update, but this will work regardless.

source: xdadevelopers