Glad you made it, that means that it is really still possible and that I have system / environment / card specific problems.
For example, I need to use set USE_NINJA=OFF, else I get this error:
  File "C:\Users\Admin\anaconda3\envs\dl\lib\site-packages\setuptools\msvc.py", line 314, in msvc14_get_vc_env
    return _msvc14_get_vc_env(plat_spec)
  File "C:\Users\Admin\anaconda3\envs\dl\lib\site-packages\setuptools\msvc.py", line 278, in _msvc14_get_vc_env
    raise distutils.errors.DistutilsPlatformError(
distutils.errors.DistutilsPlatformError: Microsoft Visual C++ 14.0 is required. Get it with "Build Tools for Visual Studio": https://visualstudio.microsoft.com/downloads/

Which is one clear difference with your settings. And in addition, I must use MKL, since else, I get “Error loading caffe2_detectron_ops_gpu.dll”, see the header of this thread - even if pytorch gets fully installed then.
At the moment, it crashes just a minute after the start, so something else has gone wrong with the command or with the cloned pytorch directory.
subprocess.CalledProcessError: Command '['cmake', '-GVisual Studio 16 2019', '-Ax64', '-Thost=x64', '-DBUILD_PYTHON=True', '-DBUILD_TEST=True', '-DCMAKE_BUILD_TYPE=Release', '-DCMAKE_GENERATOR=Visual Studio 16 2019', '-DCMAKE_INCLUDE_PATH=C:\\Users\\Admin\\Downloads\\Pytorch\\mkl\\include', '-DCMAKE_INSTALL_PREFIX=C:\\Users\\Admin\\Downloads\\Pytorch\\pytorch\\torch', '-DCMAKE_PREFIX_PATH=C:\\Users\\Admin\\anaconda3\\envs\\dl\\Lib\\site-packages', '-DJAVA_HOME=C:\\Users\\Admin\\AppData\\Local\\Programs\\AdoptOpenJDK\\', '-DNUMPY_INCLUDE_DIR=C:\\Users\\Admin\\anaconda3\\envs\\dl\\lib\\site-packages\\numpy\\core\\include', '-DPYTHON_EXECUTABLE=C:\\Users\\Admin\\anaconda3\\envs\\dl\\python.exe', '-DPYTHON_INCLUDE_DIR=C:\\Users\\Admin\\anaconda3\\envs\\dl\\include', '-DPYTHON_LIBRARY=C:\\Users\\Admin\\anaconda3\\envs\\dl/libs/python38.lib', '-DTORCH_BUILD_VERSION=1.7.0a0+4e964f3', '-DUSE_MKLDNN=OFF', '-DUSE_NINJA=OFF', '-DUSE_NUMPY=True', 'C:\\Users\\Admin\\Downloads\\Pytorch\\pytorch']' returned non-zero exit status 1.
I will probably get further when I can finally use ninja, as you can do it. That should be possible. I will start some new tries as soon as I find the time.