Having this issue and all of the documentation seems to indicate that Individual accounts should behavior just like Organization accounts. I have a friend who has an Individual account, who would like me to upload and submit a build for him. Is there no way to do this without him giving me access to his personal Apple account credentials? He's made me an Admin on his account?

We had gone that route over the weekend, as it was similar to what I had done years ago and I thought it would work. But he got an error and so I figured ask here and see if there was a better path. We used Transporter instead of Xcode archives because it seemed faster/more straight forward. But thinking about it after this response, the error was about verifying that the bundle identifier was correct, and that a temporary .itmsp couldn't be created because it was incorrect for the account. Realizing now that we didn't create the app up on AppStore Connect before attempting the upload. Did that last night, and will have him try again.

Following up here for anyone who stumbles upon this later, and as a thank you to Quinn. This worked, and the archive uploaded via Transporter was successful! Thanks for help.