Why do I see Powell Teams Advanced App in the groups created with Powell Teams?
Considering the 2 prerequisites, your teams are created by Powell Teams application. It means that the teams are not created with the right of the user who create the team but with the permissions given to Powell Teams application.
You will then see Powell Teams - Advanced Permissions application as Service Principal in the groups. It is due to the fact that the creation has been made by this application. It's not a user and it's not visible in the teams or anywhere else.