Horn does no longer sounds when locking with the key-fob; the doors lock, just no horn.

Does the horn work from the steering wheel button? Is it factory or after-market?
https://www.askmehelpdesk.com/cars-t...le-303903.html
You may have personalization feature that has been accidentally changed and may be changed back. You should search online for the owner's manual. That manual should walk you through the steps needed to customize those features.