Thanks for solving this. I had the same problem with OpenCV 4.10.0, caused by adding C:/gstreamer/msvc_x86_64/lib/gstreamer-1.0 to PATH.
C:/gstreamer/msvc_x86_64/lib/gstreamer-1.0
Doing that made CMake pull in libgstapp.a as a dependency, instead of the correct gstapp-1.0.lib.
libgstapp.a
gstapp-1.0.lib