...or maybe I should say that Synology Surveillance Station is finally fully compatible with the Wanscam K21.
In my initial review, I noted that the K21 would be detected by Onvif Device Manager, IP Camera Viewer, Onvifer, Anycam.IO and HappyTime, but not by Synology Surveillance Station.
In the latest version 8.2.8-6334 of Surveillance Station, Synology included a fix (that was developped in December last year!) which allows to capture the full functionalities of the Wanscam K21 as an ONVIF device.
This change is likely to benefit other Onvif cameras that failed to work sith SS8 before.
The Wanscam K21 can be found below 30€ at Bangood