I tried creating a 'Owner' Team account. Towards the end of the configration, at the time of 'Save' it mentions this user is already available in the project.
But, unable to see the user in the Team accounts & groups list.
When checked in the Readers & groups, I could find the user.
Should be able to add a user to the team accounts, if already available in the Reader & groups.
It will be good to see the prompt with the necessary details and asking for consent, adding user to team accounts will remove from readers & groups.