It’s likely I am doing something very obvious but unsure why this is happening, should I revert back to an older version? I have not used 3d slicer for some months and attempted to install the newest version, but cannot download basic extensions,
These all work well for me. Are you behind a hospital/corporate firewall or proxy server?
If that’s the case then report this issue to your network administrators. While they fix the issue, you can download the extensions from the Extensions Catalog website and install from file.