From one of the Jellyfin devs in the issue you linked, posted in April this year:

Now, let’s address this clearly once and for all. What is possible is unauthenticated streaming. Each item in a Jellyfin library has a UUID generated which is based on a checksum of the file path. So, theoretically, if someone knows your exact media paths, they could calculate the item IDs, and then use that ItemID to initiate an unauthenticated stream of the media. As far as we know this has never actually been seen in the wild. This does not affect anything else - all other configuration/management endpoints are behind user authentication. Is this suboptimal? Yes. Is this a massive red-flag security risk that actively exposes your data to the Internet? No.

At this point, this over-4-year-old issue has gotten posted to HackerNews more than enough times and gotten quite enough unhelpful peanut-gallery comments like those above… We are limiting this issue to Jellyfin collaborators only at this point. Most of the big items are already tracked elsewhere (specifically, unauth playback) or have already been fixed. And many other options are now open to us in a post-10.11 landscape now that we have a proper library database ready.