One thing that took me a looong time to realize is that Peertube federates weirdly - it's all under control of the instance admin, not it's users. Admins decide which instances federate with each other and then all the videos are copied between instances that have agreed to federate with each other.
But there's no way to see this in the UI, as an ordinary user!
So it's all super fragmented. Discoverability is atrocious, even by fediverse standards.
If you look at https://instances.joinpeertube.org/instances?sort=-totalInstanceFollowers then that'll help you find a well-connected instance. Then post onto that one.