Could have a look at peer tube, it is decentralised so depending on interest there may be a specific instance with the content you are looking for
I am on https://diode.zone/ which is more science / tech related, if that helps
not sure about documentaries but lets see what the community can help with
@bibliolater
it is not easy I will give you that, anything specific you are looking for and we can try and help
I will tag
@peertube
in to see if they can also help