It seems that scikit-build-core defines CMAKE_INSTALL_PREFIX to site-packages, that is, everything is assumed to by either Python files or Python C extensions. However, I need to install a C library, ...

C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Python 3.7>python -m pip install sciann==0.4.5 Defaulting to user installation because normal site-packages is not writeable ...