On 21st August 2019 Microsoft announcedthat actions in Microsoft Flow from Outlook stack, are going to be moved from using Outlook REST API v1.0 to Microsoft Graph v1.0. Along with that information there was also written, that current Outlook API 1.0 is going to be decommissioned in 1st of November 2019. So after that date all old actions in Microsoft Flow are going to be removed too.
There would be nothing wrong with this transition, moreover – it is motivated by important arguments, however together with positive aspects it has one, significant negative issue: total size of the message sent to Microsoft Graph v1.0 API and the size of each attachment cannot exceed 4MB. That means – large attachments simply cannot be sent from Flow anymore.