According to the documentation of the “syncserver” option:
Media syncing is not currently supported. You will either need to disable syncing of sounds and images in the preferences screen, sync your media via AnkiWeb, or use some other solution.
Why is that? It it especially cumbersome to implement? Are there any plans to implement it in the near future?
I was really thrilled when the “syncserver” option was introduced because I currently have a cumbersome import/export via USB by placing new cards into a separate deck that I then import into the collection after importing from the phone yadda yadda process because I don’t want to place my personal cards on AnkiWeb. If I can’t sync media I don’t see how I can use the “syncserver”. If media syncing is implemented you would get an enthusiastic beta tester for free
In my opinion TLS/SSL encryption and user authentication all have lower priority because if someone really needs it (I don’t for a private network) then they could always run a reverse proxy e.g. with nginx.