Q: How do I disable this feature in Mac Mail?

Please open mail application , then mail preferences & select general check for new messages as manually & click the get mail button in the mail tool bar to get messages .

If Mail on your Mac downloads messages only when you open them - Apple Support

In the settings if there was an option as none so, when new messages arrive the computer user  will not be able to view messages .

I think so , IMAP account settings are in such a way .

Just a thought .

Happy computing , Thanks .

i meant to say that in options , automatically , one minute , manually etc ..... . there is no option none if new mail arrives the user won't be able to check up coming mails .