Fediverse

From what i understand, it is very easy to get the content of a Peertube instance from anywhere on the Fediverse, as a viewer. For example, i could subscribe to Peertube channels from this Piefed account and have their videos pop up in my feed, and i can subscribe to Peertube channels from instances that are not federated with the Peertube instance where i have an account (i'm on makertube.net, and even though they do not federate with video.blast-info.fr, i can still subscribe to channels there and have their videos pop up in my Suscribings feed in Peertube).

The federation point some people pointed out is about discoverability, not accessibility. If two instances do not federate, you cannot see the other instance content on discover pages, but you can still access it if you know the video or the channel URL. If you stumble upon another Peertube instance, you can use a neat functionnality to "Subscribe with a distant account", where you enter your handle (username@instan.ce) and it will enable you to get access to this Peertube instance on your home account.

There is also the problem that you cannot create an account on a lot of Peertube instances, that are only there to display content (like the Blender instance) and not host users. You'd first have to find one that will let you create an account, most times manually (you fill a form and after a bit of time (hours or days) an admin validates it).

Now, for hosting video, it's a lot more complex, most times you have to get approval from admins to host things, to avoid having too much video stored on their servers, and yes most instances are quite niche. If you're a creator of anykind, makertube.net may interest you.