Hi, I'm John! I will help you with this.
Just to confirm, are you using the new Outlook for Windows? If so, please try restarting the Outlook app first, sometimes a quick restart can refresh the view and bring the folders back.
Also, when you check your Outlook on the web https://outlook.live.com do the missing folders appear there? This will help us figure out if the issue is with the app itself or something else.
Click "Add comment" to let me know.
Regards,
John J.D.