Hopefully this is what you're after. Note that I haven't used a Shared mailbox for this example, but would work the same. I'm also assuming you have a Person column in your list for the Managers. For this example, I have a Person column called Manager.
See full flow below. I'll go into each of the actions.
When a new email arrives (you would have your Shared Mailbox trigger here) is set to Include Attachments and Only with Attachments.
Get items uses the following Filter Query to retrieve the manager that sent the email.
Manager/EMail eq '@{triggerOutputs()?['body/from']}'
Apply to each Attachment iterates over each of the attachments.
Get Attachment uses the Message Id and Attachments Attachment Id to retrieve the content from the current attachment.
Apply to each Manager will iterate over the Manager that was returned in Get items. Note that even though we have a loop here, it will only iterate once since only one Manager should have been returned.
Add attachment adds the attachment to the Managers record. It uses the ID and Manager Display Name from the Get items action, and the Attachments Name and Content Bytes from Get attachment.
After the flow runs, you should see the attachments added to the Managers record.
