You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.

gns3_cx_Freeze
4.3.5

This version was deleted from PyPI around 2023-10-10. Installing fails with:
$ pip3 install gns3_cx_Freeze==4.3.5 ERROR: Could not find a version that satisfies the requirement gns3_cx_Freeze==4.3.5
View other deleted versions of gns3_cx_Freeze

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/2023-10-09/ \ gns3_cx_Freeze==4.3.5
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Or, download files manually

And install manually via pip:
gns3_cx_Freeze-4.3.5-cp35-cp35m-macosx_10_6_intel.whl (523.4KB)
gns3_cx_Freeze-4.3.5-cp35-cp35m-win_amd64.whl (1,019.9KB)
gns3_cx_Freeze-4.3.5.tar.gz (58.2KB)