https://learn.microsoft.com/en-gb/answers/questions/5605606/how-to-stop-ms-teams-launching-at-startup-and-rein

Apparently:

This behavior is usually caused by two things:

• A background installer from Microsoft Office called the Teams Machine-Wide Installer, which automatically reinstalls Teams for each user.
• Windows 11’s built-in Chat feature, which is powered by Teams and may reinstall the app during updates or restarts.