The hls_video.h library has been deprecated and all functionality is provided for in the Vitis Vision libraries. Also, the Vitis HLS and Vivado HLS tools no longer provide a OpenCV installation as of the 2020.1 release in order to avoid library version conflicts such as you are encountering. Because Vivado HLS hls_video.h is no longer supported, and the Vision libraries in the Vitis HLS flow are the only path going forward, I recommend you upgrade your design to use these.
I think this will still help you create a script even though you aren't using that exact flow. However, you mention OpenCV version 4.x. While the OpenCV library is never necessary for the implementation of the Vision kernels, it is used in the example design testbenches that are provided. The version used for verification was 3.3, so any 3.x version should work directly. With version 4.x, some of the OpenCV library functions have changed, and so the examples designs may not work without modification if you use that version.