Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
You probably set some rules to divert all mails to Junk folder. Open Mail > Preferences. Then click on Rules tab and delete all rules there.
Then click on Junk Mail tab and set Mark as junk mail, but leave it in my Inbox under When junk mail arrives heading.
Let me know how it goes please.