Hmm, my understanding was that FQDN means that anyone will resolve the domain to e.g. the same IP address? Which is the case here (unless DNS rebinding mitigations or similar are employed) — but it doesn’t resolve to the same physical host in this case since it’s a private IP. Wikipedia:

A fully qualified domain name is distinguished by its lack of ambiguity in terms of DNS zone location in the hierarchy of DNS labels: it can be interpreted only in one way.

In my example, I can run nslookup jellyfin.myexample.com 8.8.8.8 and it resolves to what I expect (a local IP address).

But IANA network professional by any means, so maybe I’m misusing the term?