sharedWithMe returns only one item

This is a known and subtle behavior difference between delegated (user) tokens and application-only tokens in Microsoft Graph, and it explains exactly what you’re seeing.

Short answer…

/drive/sharedWithMe does not fully work with application (client credentials) tokens.
It is designed to return items shared with the signed-in user, and only delegated user context is fully supported.

Graph Explorer uses delegated permissions, while your standalone app is using application permissions → hence only one item (or an incomplete set) is returned.

Your permissions are correct
Your request is valid
The endpoint is not supported for application-only tokens

This is expected behavior, not a bug.

Final recommendation

If your scenario is user-centric (which sharedWithMe is):

Switch to delegated authentication

My answers are voluntary and without guarantee!

Hope this will help you