In general, FormAssembly does not have access to Salesforce Auto-Numbering, Formula, and Lookup fields. This is due to Salesforce's API and the types of fields that FormAssembly is able to access.
However, there are occasional situations where these fields may be accessed.
For example, you can use Salesforce Lookup fields within a lookup in your connector (e.g., with Record IDs).
You can also use Auto-Numbering and Formula fields in the Salesforce Prefill connector. However, these field types cannot typically be written to in the Submit connector (especially if they are listed as "read-only" fields in the Salesforce Objects Reference).