When adding a user to a private chat, the user who participated so far can check
If you add another user to a one-to-one chat (private chat), a new chat is started and the added user cannot see the history.
In group chat, you can choose whether to share the history, so when you try to add a user to a private chat, I want to add a function to whether to share the past history.
Rebekah Cox commented
Yes please - would also like this function! Has also been asked about here: https://techcommunity.microsoft.com/t5/microsoft-teams/private-chat-add-people/m-p/233555