@Cadair and I were pleased to notice that you use a fork of the openmp_helpers.py file from astropy in scikit-learn:

https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/_build_utils/openmp_helpers.py

We just wanted to let you know that we have been working on generalizing the helpers we use in astropy and have now released a lightweight and general package called extension-helpers which includes the OpenMP helpers. This package is intended to be used as a build-time dependency in a pyproject.toml file if/once you switch to using this to specify build-time requirements.

Would you be interested in contributing your fixes to openmp_helpers.py upstream to extension-helpers, and using extension-helpers as a build-time dependency? Let us know if you have any questions about extension-helpers! (the GitHub repository is at https://github.com/astropy/extension-helpers).