I wonder, does the Apple Watch series 10 have a hidden port?

When it was first discovered the techie wannabes drooled over the possibility of using it for something other than diagnostics. Never happened and it was removed in the series 4 and later watches, over ten years ago.

Here’s what ChatGPT has to say about the matter.

Details About the Secret Port:

• Models with the Port:
  • Found on Apple Watch Series 0 to Series 3.
  • Removed from Series 4 and later.
• Purpose:
  • Used by Apple for diagnostics, firmware restoration, and testing.
  • Some third-party developers attempted to use it for charging and data transfer, but Apple blocked such uses.
• Covering:
  • It's hidden under a small metal plate in the watch's band slot.

Apple Watch 10 doesn’t have any hidden ports, but it has the traditional magnetic charging port. Apples design is quite minimalist. so there aren't any visible ports or connectors for accessories aside from the charging point.

no, it would be rather wasteful to add a connector which were hidden as as such not used by most users

you can see how the watch looks on the inside on this page

Apple Watch - Series 10 (46mm) Screen Replacement - iFixit Repair Guide