In 2017, Google introduced the PiP (picture-in-picture) service for owners of paid RED/Premium subscriptions. But it looks like the regime is coming soon
Who is already available
In June 2018, US residents were able touse the function even without a paid subscription. For some reason, Google then forgot about the rest of the countries. Now users from Italy have noticed that this mode has also begun to work for them. It may be available in other European regions in the near future. However, only for owners of smartphones with an OS version starting with Android 8.0 Oreo.
The PiP function allows you to minimize videos toa small window and at this time scroll through another application. You can enable it in YouTube settings, then open the video and go to another application or to the desktop. The author of the video can restrict access to the mode. Exactly when it will be available to everyone is still unknown.