Do yourself a favor and move away from UPnP and install LMS GitHub - epoupon/lms: Lightweight Music Server. Access your self-hosted music using a web interface.
You can run it in 2 seconds in a container on your Synology and will find it’s much better.
Anyway this is a duplicate there’s no plans to support UPnP as a server as it’s just the worst possible protocol and does not fit the needs for Symfonium.