I've installed all that the documentation said is required:
$ pip list
Package Version
------------ -------
cmake-format 0.6.13
cmakelang 0.6.13
pip 21.0.1
PyYAML 5.4.1
setuptools 49.2.1
six 1.15.0
$ clang-format.exe --version
clang-format version 11.0.1
However, cmake --build build/standalone --target format works.