FIXED / RESOLVED - Error CC-800
I'm posting this in a new thread in hopes that others who encounter this error will search and find this to help them resolve their issue.
When asking how to troubleshoot the CC-800 error, the user will typically be referred to a support article at this link. Those are necessary steps, but in many cases it will not resolve your issue unless you incorporate another very important step.
After you have deactivated your accounts and removed institution and account number info from the details of the account, then SIGN OUT of your Quicken ID and leave it signed out OVERNIGHT.
The next day, open your Quicken data file, sign in with your Quicken ID, then re-add/link your accounts.
This extra step helped to resolve my issue.
Props goes to @binary512 for his comment in this thread which helped me fix it.