How can I activate the popout window as in Opera?
or does not exist here
@richirm The feature has been requested, but is not implemented at this stage.
The feature does not exist in Vivaldi yet.
However, as of version 61, Chromium has a picture-in-picture video flag present and this feature is being actively developed by Google. From what I understand, it is still quite nascent (I haven't been able to get it to work despite enabling the flag), but the feature will be built up. I bet that the Vivaldi team will let the Chomium team do the hard work on this and focus on other areas.