Multi-window is, without a doubt, one of Android 7.0 Nougat’s biggest feature additions. Samsung pioneered the idea a few years back, but it’s finally on Google’s version of Android. Just like with numerous other OEMs’ implementations, many apps, such as Pokémon GO, are restricted from launching into Nougat’s multi-window; however, Google has added an option to enable any app to do so in Developer Options, which can be found in the Settings menu.
[Guide] How to use Nougat’s multi-window with apps that don’t natively support it, like Pokémon GO was written by the awesome team at Android Police.