Users or Administrators cannot access these hidden files. Teams stores an individual’s chat history in a hidden file in the users mailbox which is not accessible via OWA or Outlook. Here are some of the use cases I worked on (probably not the exact case as yours but you might get some clarity here about where to look for) The answer depends on the type of content/period that you need. An uncommon but definitely one of those once in a while query from the HR or compliance/security leadership you will get is “Can we search for Microsoft Teams chat” in Office 365.
