The problem is that the Google Cloud console cannot identify your email account. You should try changing the primary email address associated with the project:
change the primary email address associated with the project
To change the email address associated with your project, you must first add another account with the email address that you want to set as the primary email for your owners. This is set in Permissions> Add Member. After you add another user to the permissions, they must access the project in order to set their email address as the project email address.
We hope that changing your email address resolves your issue.
As you mentioned, you can only set the email address associated with the current user. In your case, when you added your iCloud email address and replied to the email message, Google detected who you were logged into with as it was determined to be the same account that was already associated with the project.
You must add an additional (Google) account to add an employee and change the corresponding email address.
The last thing to check is to provide an email address at the top of the consent screen. This is the first element that you can set in the form and drop down.
Finally, if all else fails, you can try setting up your project from the classic Google API console .
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