For packages from PyPI `conda-lock` does not fall back to older, viable versions

[imLew]

Checklist

• I added a descriptive title
• I searched open reports and couldn't find a duplicate

What happened?

Context: a PyPI dependency in my conda env requires a major version of a recently updated package.
(The package in question is dark-matter and the requirement is mysql-connector-python>=9.0.0, on Jan 21st 2026 version 9.6.0 was released on PyPI.)

conda-lock fails with RuntimeError: Unable to find installation candidates for mysql-connector-python (9.6.0)
When I try with conda env create --file version 9.5.0 of the package is installed.

Since conda also doesn't install 9.6.0, it seems that there really is some issue that's not related to conda-lock, however, unlike conda, it is not able to figure out that there are version available that satisfy the requirements.

Additional Context

conda-lock installed from PyPI with uv

$ uv run conda-lock --version
conda-lock, version 4.0.0

$ mamba --version
2.5.0

$ conda --version
conda 25.11.1

A minimal conda-env.yml that can be used to produce the result:

channels:
  - conda-forge
dependencies:
  - pip
  - pip:
      - dark-matter

uv run conda-lock lock -k explicit --filename-template "{platform}-{input-hash}.conda-lock.txt" -f conda-env.yml -p linux-64

I also tried with -p osx-64, but got the same error.