We recently setup service accounts to backup Exchange Online in O365, and we've noticed that these service accounts have started automatically joining teams in Teams.  Users are contacting the help desk because they are seeing these accounts joining their chats.  Does anyone know where to look to prevent these service accounts from joining chats in Teams?

Thanks,

For private goups (teams) to backup service account should have the owner rights so if team mailboxes are added as a content in the sublclient then while backing up we have to added service accounts as OWner of those teams.

from the subclient MB list remove these team mailboxes to not to assign the rights.

i hope this will help you to understand the root cause behind addig the service account as owner of teams.

From the subclient you can choose the option to exclude from Teams.