Same here, brand new 7480 AIOs, Support Assist or Command update, both pre installed and then updated don't work. I did BIOS update from F12, then remote update via dell website Driver updates work going to dell website, that then uses Support Assist. However, both installed Apps Support Assist and Command Update 'nag' users occasionally to run, but both fail to get updates, not a good user experience.
I have 3 different systems that when I run Dell Command Update and try to check for updates fails with "Application Error An unexpected error occurred during the last action, the operation was aborted". After this it's activity log has an entry with "Update operation error: One or more errors occurred".  This could be related to Windows 10 March 2021 updates. I have a habit of running Win 10 updates and then also checking MS Office, system drivers, etc. An this month I've hit this error. Of the 3 systems 2 are Win 10 20H2 and 1 is still 2004.They are all different hardware being 2 laptops and 1 desktop. Anyone else seeing this?  
Dell Command Update gets Application Error