Custom object or custom field not visible in Data Loader

To resolve the issue of a missing custom object or custom field in Data Loader, verify the following four areas in Salesforce Setup:

1. Object Deployment Status
The object's deployment status must be set to Deployed. Objects in In Development status are not visible to most users. Navigate to Setup > Object Manager, open the object, and verify its deployment status.

For more, see Deployment Status for Custom Objects and External Objects.

2. Profile or Permission Set Object Permissions
The user's profile or assigned permission set must grant Read, Create, and Edit access to the object. Navigate to Setup > Profiles (or Permission Sets) and verify the object permissions.
For more, see Edit Object Permissions in Profiles.

3. Field-Level Security
For custom fields to appear in Data Loader, Field-Level Security must be enabled for the user's profile. Navigate to Setup > Object Manager > Fields and verify field visibility for the relevant profile.
For more, see Field-Level Security.

4. Data Loader Display Setting
In Data Loader, ensure the Show all Salesforce objects checkbox is selected when choosing an object. Without this setting, custom objects may not appear in the object list.
For more, see Insert, Update, or Delete Data Using Data Loader.