NucubePlayer, not a server
“I use Navidrome or another Subsonic server, and I want a player that does not add one.”
Play the library you already have
If the files live in folders, on an SMB or NFS share, or on a DLNA server, Nucube plays them there. No Nucube server. Files are never moved or retagged.
Stay with a Subsonic server if the library should be a service
Navidrome and other Subsonic-style servers are a remote music backend — multi-user access, transcoding, OpenSubsonic clients, listen-from-anywhere. That is a different product class from a player. Stay if you want the library as a service. Try Nucube if you want to play what is already on the LAN or the disk, without adding a music-server layer.