Perhaps this Article from Apple will supply the requested information on Follow Up and how it should work
Reply to, forward, or follow up on emails in Mail on Mac
Excerpt from above link
Get reminded to follow up on emails with no response
If you send a message and don’t receive a response in 3 days, the sent email automatically resurfaces to the top of your inbox to help you remember to follow up.
- To ignore a follow-up suggestion, swipe right on the message in the message list.
- To turn this feature on or off, choose Mail > Settings, click General, then select or deselect the checkbox next to “Enable message follow up suggestions.”