See the <x id="START_LINK" ctype="x-a" equiv-text="<a target="_blank" href="https://docs.joinpeertube.org/#/use-library?id=playlist">"/>documentation<x id="CLOSE_LINK" ctype="x-a" equiv-text="</a> "/> for more information.
You can comment using an account on any ActivityPub-compatible instance. On most platforms, you can find the video by typing its URL in the search bar and then comment it from within the software's interface.