How to hide bottom navigation bar in Youtube app?
The Xposed module L Tweaks supports the feature of removing the bottom navigation bar of Youtube and several other apps.


Install L Tweaks. After installing the module, open it, then click Google.


Google apps are listed with features that L Tweaks can enable/disable. Go to the bottom to find Youtube. Enable Remove bottom bar


Before opening Youtube, force stop it. Open Youtube, the bottom navigation bar will no longer be shown. 


To access Home, Trending, and other options, swipe from the left as you do for Google .Play




The module is also available in Google Play Store and has other features.

Note: The device must be rooted, and have Xposed framework installed to use the module correctly.

Disclaimer: I am not related to the app's developer; I am just a user.