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from the doc

CAP_PROP_SETTINGS Pop up video/camera filter dialog (note: only supported by DSHOW backend currently.

Maybe opencvsharp uses cv::CAP_DSHOW as default backend for VideoCapture. Try using:

VideoCapture capture(0+cv::CAP_DSHOW); // open the default camera using DirectShow
if (!capture.isOpened())  // check if we succeeded
    return -1;
capture.set(CV_CAP_PROP_SETTINGS, 1);

And the doc says

Backends are available only if they have been built with your OpenCV binaries. See Video I/O with OpenCV Overview for more information.