Gmail suddenly stopped receiving emails but sending works fine. What's going on?

Run these in order, one is almost always it: 1) Check Spam, All Mail, and your Filters (Settings > Filters), since a rule can auto-archive or delete incoming mail silently. 2) Check storage, a full Google account (15GB shared across Gmail/Drive/Photos) stops delivery cold and is the most common cause. 3) Check Settings > Forwarding and POP/IMAP for an unexpected forward. 4) Try the web version to rule out a phone-app sync issue.

Storage is the big one people miss. If your 15GB is full, senders can even get a bounce. Clear big attachments or free up Drive/Photos and mail flows again.

A rogue filter is my bet given that sending works. Someone set up a filter that skips the inbox. Settings > Filters and Blocked Addresses, delete anything suspicious.

Also check you have not accidentally blocked the sender, and that the app has sync permission if it is only the phone that looks empty.