Outlook suddenly stopped receiving emails but I can still send. What's wrong?

Run these in order: 1) Check Junk/Spam and any Rules (File > Manage Rules) that might be auto-moving or deleting incoming mail. 2) Check if your mailbox is full, a full account stops delivery. 3) Check the Focused Inbox filter, new mail might be landing in 'Other', not 'Focused'. 4) Make sure 'Work Offline' isn't switched on (Send/Receive tab), it's a classic one. 5) Try Outlook on the web to see whether it's the app or the account itself.

Focused vs Other trips so many people up. Your mail might be arriving perfectly fine, just sitting in the Other tab. Check there before anything else.

'Work Offline' being on by accident is my number one culprit for 'sends but won't receive'. It's right there on the Send/Receive tab, easy to hit without noticing.

If none of that works, a rule someone set up is usually the villain. File > Rules, delete anything that touches incoming mail and test again.