[Mike Compas]

I just may have found an alternate end process to solve this problem: reinstall a previous version of iTunes.

Just as noted in Xavier’s message above, you most likely will need to disable SIP via Recovery Mode. This is important because you’ll need to manually delete the MobileDevice.framework file in order to replace it with an older version. Simply reinstalling iTunes (12.8.2) without first deleting the framework will not suffice, since installer packages will not overwrite certain files if a newer version is already present.

Manually restoring the MobileDevice.framework file from a backup may not be sufficient if the backup is not recent. It’s my guess, but there may or may not be compatibility issues with the framework file (if it’s too old) and the iTunes version is newer. In my specific case, my last backup is from almost two years ago, so manually replacing the framework file was not an option for me, despite STILL being on Sierra (10.2.6) for eGPU reasons.

Lastly, to note, the older framework file that works is listed as version 988.222.1 (created Jan. 10, 2019), and the offending version that breaks Cinema 4D is version 1190.9.1 (created Aug. 29, 2019). You can check the version numbers via Get Info in the Finder.

Nonetheless, backup your machine regularly for your safety and sanity! Thank you all for your solutions and bringing this to light.

You can download older versions of iTunes from Apple’s Support page: https://support.apple.com/downloads/itunes