How can I get IDM grabber to work with video online websites?

Please note that IDM site grabber is not designed to download streaming videos from web sites. IDM is designed to show the video download panel when it sees a video download request from a web player.

But you need to open a web page with video in your browser, find and press on a play button in a web player, find and select quality in the web player if necessary, and only then the web player will make the video download request that IDM can record.

IDM grabber cannot do it automatically, we would need to develop some artificial intelligence to press all play buttons, and it's not that easy.