I am having the same issue, too. For some reason my packages are exporting right now as .zip rather than .imscc files. I do have an older .imscc file that downloaded successfully and that one can be imported to other courses... but apparently this is not working this time.
I clicked "Export course content"; the file prepares and starts downloading, but it downloads as a .zip. I am using MacOS Ventura 13.7.5 with Firefox.
I have tried to change the extension from .zip to .imscc, as advised. When I proceed with the import, the result is "Failed" due to "Unsupported content package."
My suspicion is that something in my OS is converting the imscc to zip and losing some kind of important format information in the file wrapper. Is this some kind of known issue on Mac?
Rodney