Slack DM’s

Its been there since a long time. Nothing to be surprised of, slack explicitly mentions this that in some versions the workspace admins can have access to all types of chats including the DMs.

Does this apply to Teams too?

Always assume your employer can track your office laptop and phone

All enterprise communication apps have this feature

Be it slack or any other enterprise employed tools for collaboration,admins have the capability to export chats. Avoid anything that can possibly bring trouble