pyside6-essentials
6.4.0
This version was deleted from PyPI around 2024-10-15. Installing fails with:
$ pip3 install pyside6-essentials==6.4.0
ERROR: Could not find a version that satisfies the requirement pyside6-essentials==6.4.0

Install through StableBuild
You can install this package from StableBuild's PyPI snapshots from before the version was deleted:
pip3 install \
-i https://YOUR_API_KEY.pypimirror.stablebuild.com/2024-10-14/ \
pyside6-essentials==6.4.0
Sign up for StableBuild to get an API key (it's free and takes <60 seconds!)
Or, download files manually
And install manually via pip: