A bunch of threads and info on this down in the
Smart Controller sub-forum - but a few key things:
Make sure you have the latest version of DJI Assist 2 - you HAVE to use this - and make sure you have the xxxx.08 version - this seems to be the root of the issue for most folks
Some reported needing to uninstall previous versions of Assist 2 and reinstall the new version
Suggested to use the USB-C cable that DJI provided with the
SC for charging purposes to use to connect to your computer for update.
Some reported issues with USB3 vs USB2 ports...
I was able to successfully update mine via my Macbook Pro - I did have to restart the initial software download a few times as it kept dropping the internet connection, but once it downloaded to the Mac the rest of the process went smooth