How to change the URL after Syno Community package installation?

[TheDreadPirate]

Honestly, this sounds like a DSM issue.  You may have better luck asking on their forum how to change the link in the DSM dashboard.

The base URL field would append the URL.  You'd need to update the reverse proxy in addition to that setting in Jellyfin to make use of it.  Not recommended if you can help it.

This is NOT a DSM issue.  If Reverse Proxy is established on Synology NAS and you install synocommunity jellyfin, the DEFAULT URL created by Jellyfin uses the main domain name for that Synology NAS.  When Jellyfin is installed, there ISN'T a field where you can type in the Reverse Proxy URL and port.  Why is the ONLY answer, when someone is stumped is:  "Sounds like a DSM issue".  And NOWHERE ON THE Jellyfin dashboard is a field to change it!!!!!!!

Because it isn't a Jellyfin issue.  As you've said, you've setup the DSM reverse proxy.  THAT is responsible for determining the URL used.  Not Jellyfin.  Jellyfin is hidden behind the proxy and Jellyfin itself does not and cannot manage the URL that the DSM reverse proxy responds to. The proxy is an entirely separate app gate keeping requests to Jellyfin.

Additionally, the SynoCommunity package is not an official package.  Whatever URL that configures with the DSM reverse proxy is probably tied to the package itself and not something we can change.

Jellyfin is pretty "dumb" when it comes to web requests.  It responds to any requests on its configured port.  It isn't like nginx or apache or some other apps that look at the requested URL used to determine how/if to respond.

If the requests aren't arriving, Jellyfin can't do anything about it.