I can access the web interface via: http://IP_SYNOLOGY:3373
I would only access bitwarden locally.
I road that bitwarden requires https - this I solved with synology reverse proxy.
The web interface is now accessable via: https://SYNOLOGY_DSM_NAME:3373
(login and bitwarden works !)
With the windows and macOS client I can access my bitwarden server.
For this I use the server address https://SYNOLOGY_DSM_NAME:3373 angegeben.
But with the ios App I get this error:
An error has occurred.
Exception message: An SSL error has occurred. A secure connection to the server cannot be established.