Unable to connect new American Express account - error NOT the one that's been in alerts here

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The only way I can add the account is manually. Any attempt to actually log in/connect to American Express results in the exceptionally unhelpful error, "Sorry. We encountered an error. (It's not your fault)."
Very nice to be advised that it's not my fault. Very useless not to give an error code so it can be diagnosed.
How do I find out what's wrong? I am assuming - perhaps naively - that it is unrelated to "RESOLVED 5/16/22 American Express - CC-503/103", since I don't get an error code.

Quicken Premier v R40.21 Build 27.1.40.21 Windows 10 Enterprise.
Size of QDF file: 93186k
Accounts: 22
Categories 329
Memorized Payees: 22
Securities/Max ref: 463/463
Transactions: 33695
Total memory: 2097151K
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