Does "License unknown" mean "All rights reserved"?

If it instead means “CC-BY-SA-ND-NC or free-er”, that means that every video published on Peertube is automatically under a CC-style license. If that is the case, I think that is a potential obstacle to growth; after all, there are a lot of content creators who want to let people watch their videos for free but remain “owner” of their work in a way that includes having their work only on their channel and not have it be freely distributable.

I think it’s clear : It means that license is not known, so you can’t use it as a CC-Whatever license.

That would be my intuition, yes. But the fact that the only license options available are CC-style licenses seems to imply that you can or at least should only publish videos under a CC-style license on Peertube.
I guess you’re right, though: if you distributed something that says “license unknown”, you could hardly expect to get out of a copyright suit with “but all the license options were…” as your argument.
I would still like to know why there isn’t an “all rights reserved” option. Or I guess not all rights reserved, because you don’t reserve the right to view it online for free and to give someone a link to it.

O, I misunderstood your question. I though you were talking about visible videos uploaded by someone else.
The fact that available licenses are only CC- is strange, you’re right. Maybe each instance can configure which licenses are available, I don’t know ?

I’ve looked around at multiple instances. In the license search filter, there are only CC-style licenses to choose from.

In France, a work of which the copyright holder is known but not the license, is automatically under the copyright laws (which is equivalent, I think, to “All rights reserved”). In other countries, I don’t know.