I think what those terms mean is that you can't build a third party service that makes use of the Connect API to provide services. But of course you can use the Connect API to submit your own apps for notarization.
travisbigarmor
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NLTeo's post below worked for me.
This worked for me. I had a CI/CD pipeline that was using app specific login credentials to submit a binary to be notarized. This morning I switched to Apple Connect API keys, and now the submission is successful.
It appears that Apple doesn't know that their developer services authentication for app specific logins is not working.