Ich vestehe nur Bahnhof @audition84 😅
I translated your text into English because I don’t speak or understand Spanish:
I have a Synology NAS server that is connected to the Quickline router with an ethernet cable and I am having trouble implementing PLEX as a server for external internet. UPNP doesn’t seem to work, is there any way to open ports in the cabinet configuration?
thank you very much
You cannot set anything on the cable modem if the cable modem is in bridge mode.
How is the bridge mode setting on your cable modem: active or not?
You can check this in the Quickline Cockpit or, if necessary, ask Quickline or the cable network operator.
It is best to operate the cable modem in bridge mode and then use your own router. There you can configure all port forwardings together with the Synology NAS.