A question about how best to set auto-replies for Exchange Online shared mailboxes to respond to messages arriving during a public holiday gives another chance for PowerShell to show how useful it is. You could do the work with Flow, but PowerShell is more flexible and capable when dealing with multiple shared mailboxes.
https://office365itpros.com/2019/07/29/setting-auto-replies-shared-mailboxes-powershell/
