From the issue you shared:

Thank you b4too - unless something new has been uncovered - which if so should be reported to us via our responsible disclosure policy - it is NOT possible to arbitrarily enumerate all media on a server without authentication, and saying as much is massive fear-mongering

Unfortunately that doesn’t seem possible, afaik. Although you could always create a zip file with a password, and share it with an open link (anyone with the link can download it, no need for account).

Maybe something like xbackbone? I’ve used it to share small-ish files and it works fine; I don’t know how much of a pain it would be to use for a group of people, but as long as everyone has an account they should be able to access files with a link.

I guess the advantage would be to have a more updated copy, because the ones on kiwix are one year old.

I’m guessing that it notifies you before the cert expires, because I already have a great notification system for the server not working: I’ll always get a text from a friend within minutes asking why it’s not working :P