Until recently, it was possible to send emails with file attachments from SharePoint using the Office365Outlook connector. Following a recent update (in May 2021), this is no longer possible.

Taking the example of a SharePoint list item with one or more file attachments, if we add a card to a form and add a button with the following formula, the result today is that the email will send, but will not include the file attachment(s).

Office365Outlook.SendEmailV2(
      "[email protected]",
      "Message subject",
      "Message body",
      {Attachtments: RenameColumns(
                     ThisItem.Attachments,
                     "Value",
                     "ContentBytes",
                     "DisplayName",
                     "Name"
        )
    }
)

Note that the Mail connector still works and still sends the attachments successfully. Therefore, it appears that this is a problem that affects the Office365Outlook connector.

Mail.SendEmailV3("[email protected]", 
                 "Enter the email title here", 
                 "Enter your email message here",
                 false,
                 {
                    files:First(ThisItem.Attachments).Value,
                    filenames:First(ThisItem.Attachments).DisplayName
                 }
)

Since SharePoint is a highly popular data source for storing files, and the ability to send file attachments plays a key role in many business apps, I hope that this is something that Microsoft will fix.

I've added a post in the ideas forum, and I would encourage anyone who values this feature to vote for the idea beneath.
https://powerusers.microsoft.com/t5/Power-Apps-Ideas/Fix-bug-Sending-email-messages-with-the-Office365Outlook/idi-p/925808#M33655