Keep in mind that streaming video likely translates to a read-mostly and sequential-read workload for the underlying storage, and that's really an ideal use-case for storage (you can do stuff like file-system caching, stream buffering and file read-ahead).
Things like nextcloud/owncloud are a lot more random-io-bound, if you think about it.
Jellyfin (NET Core backend with SPA client) runs quite well off my Pi4, even without hardware decoding.
If the device can stream 1080p video, it should be able to serve an online file explorer.