Hi,
I'm Rodell, Independent Advisor and a Microsoft User like you. Let me help you out with your concern.
If you're using Windows 10:
To stop Teams from launching automatically, click on Start / Settings / Apps / Startup. Turn off Microsoft Teams.
For MS Teams settings:
Settings. Uncheck Auto-start application. While you’re there, also uncheck On close, keep the application running and Register Teams as the chat app for Office.
Launch the Task Manager, click the “Startup” tab, locate “Microsoft Teams” in the list, and click “Disable.”
Let me know if that worked out well for you. Feel free to ask me if you need further assistance.
Regards,
Rodell