Hi this is the exact same problem I reported a day ago here: RoonBridge update error
I tried this with roopieee, volumio and a freshly setup Raspbian installation with RoonBridge installed manually. All show the same error being not able to access the update server due to the TLS issue.
05/09 23:49:16 Warn: [appupdater] Couldn’t connect to update server: System.Net.WebException: Error: ConnectFailure (TLS Support not available.) —> System.NotSupportedException: TLS Support not available. —> System.NotSupportedException: No such TLS Provider: `btls’.
Update: My device running RoonBridge is connected via Ethernet cable. No WiFi involved. But the same TLS error occurs as well.