Good news, YouTube PiP mode is rolling out to non-premium user that resides out of US
YouTube PiP Mode
YouTube PiP Mode is a YouTube app feature that allows users to watch YouTube videos in background after exiting the YouTube app.
This feature was initially available only to Premium users but around June last year, it was made available for non-premium users in US and now after about 9 month, the feature is coming to everyone either in US or outside of it. Though this feature works on devices running Android 8.0 Oreo or later.
How To Enable YouTube PiP Mode
Open YouTube app
Go to YouTube Settings > General