I have confirmed that the scope does indeed show up in the Google sign-in that's shown to users.

However, it does not grant access to resources that are available to the .../auth/youtube.readonly
scope, which seems to be the scope with the lowest permissions otherwise.
I have also found that the scope is not in the official API reference, or in this list of scopes. As I have not been able to find any more information about the scope, we must assume in the absence of evidence that it cannot be used (by ordinary users) to access YouTube resources, downloading your own public YouTube videos or otherwise.
I can see this answer being improved by any of the following:
- A proof that it is in fact possible to access resources with the scope
- An official statement concurring with the answer
- A proof that shows systematically that none of the API endpoints accept the scope
EDIT: Before any points are confirmed officially by Google, it is important to note, that as per Developer Policies (as @stvar pointed in the comment)
Undocumented Services
You must not use undocumented APIs without express permission. You
must access data from YouTube API services only according to the means
stipulated in the authorized documentation of that YouTube API
service.
You must not reverse engineer undocumented YouTube API services or
otherwise attempt to derive the underlying source code of these API
services.