This topic was created in 2019 and nextcloud has evolved quite a bit since then. I’d be interested to learn what folks are doing with Nextcloud 21 and how you are contemplating using it in conjunction with Discourse, in a “groupware” context.
From my understanding, the answer to the question in the OP:
is YES. Discourse is a discussion platform, while Nextcloud’s original super power is about file syncing and sharing: https://nextcloud.com/files/
Maybe the answer is to go back to Nextcloud and see if there is an appetite for leveraging Embed Discourse comments on another website via Javascript. It could be offered as an alternative to Nextcloud comments. Right now Nextcloud looks like this in the sidebar:
With embedding discourse comments, you’d be able to click a link to start a topic in Discourse to start talking about any file or folder, and see all the replies. The topic will have a link back to the nextcloud file or folder.