Man pages matching name mongoc_client_encryption_opts_set_kms_credential_provider_callback in section 3:

mongoc_client_encryption_opts_set_kms_credential_provider_callback.3.en	debian 12 / libmongoc-doc
mongoc_client_encryption_opts_set_kms_credential_provider_callback.3.en	debian 13 / libmongoc-doc