Hi there sengseng,
If you are not being reminded to follow up on emails in the Mail app on your Mac, first ensure everything is set up correctly using these steps from Reply to, forward, or follow up on emails in Mail on Mac - Apple Support
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.”
If this setting is enabled and this continues, please provide more specifics on the issues you are experiencing so that we can continue to isolate this behavior.
Cheers!