(1) Teams Apps Studio: It's not for building Apps, but for creating the packages to deploy Apps in Teams.
(2) Power Apps Studio in Teams: It's for building Power Apps in the scope of Teams, i.e, Microsoft Dataverse for Teams. A Power App create in Power Apps Studio in Teams cannot be used outside of Teams.
(3) "Global" Power Apps Studio: It's for building Power Apps that can be used standalone through the browser, that can be deployed to Teams as a Personal App or that can be embedded in Teams through a Power Apps Tab or in a SharePoint Site through the Power Apps Tab