This release is a major new release with additional functionality and backwards incompatible changes.
There are breaking changes to the v3.0.x version in the release.
See release and update notes - https://earthgecko-skyline.readthedocs.io/en/latest/releases/4_0_0.html or
https://github.com/earthgecko/skyline/blob/master/docs/releases/4_0_0.rst
UPDATE - ensure that you install bin/pip3.8 install gevent==23.9.1 in the Skyline Python virtualenv after installing or upgrading Skyline