If you see the error as shown in the above screenshot, please try this: instead of clicking on the sample URLs on this page, copy the URL and paste it into your browser.
The above 2 sample URLs can prevent screen capture in Chrome on Windows 10. If the same content does not prevent screen capture on another device or browser, it is really a client implementation issue. For example, the above samples can prevent screen capture on Chrome/Windows 10, but it does not on Firefox/Windows 10.
I don't think you should expect Widevine can prevent screen capture on any Widevine-equipped client.