My testing confirms that the IGB zip file is functioning properly and that I am able to unarchive the file as expected. This is true for the IGB 9.0.0 zip file and the IGB 9.0.1 release candidate zip file.
However, when testing the 9.0.1 release cadndidate's zip file, I noticed that it contained an unnecessary folder structure when unzipped:
"opt/atlassian/pipelines/agent/build/content"
The file structure for the current live version of the IGB zip file (9.0.0) is "IGB/content", which is much more user-friendly.
Since this original issue relates to the current IGB zip download not working, I am going to close this issue and track the issue with the IGB zip folder structure in IGBF-1178.
I just tested this on my Linux machine and was able to download and extract the .zip and run IGB.
The second link does not work, to test I followed the first link and selected 'zip file' under 'Zip Download'