To send to the user, as 1-to-1, I used the activity Create a Chat and put the email there, then that gives me as output an conversationId, and I use it in Group Chat field of Post adaptive card and wait for a response 2 and Update an adaptive card in a chat or channel.
ConversationId = @outputs('Create_a_chat')?['body/id']
MessageID = outputs('Post_adaptive_card_and_wait_for_a_response_2')?['body/messageId']



The group chat field can be a conversationId as 1-to-1, because you retrieve the conversationId from the Create Chat activity. (And don't worry, if you use the activity, the conversation on teams will always be the same, because if teams has a conversation already between those 2 people, it will use that one. If not, it creates a new chat with that person.)