Do I need a state nomination for the subclass 491, or can a relative sponsor me?

The 491 has two routes to the required support. You can be nominated by a state or territory government agency, or you can be sponsored by an eligible family member who lives in a designated regional area.

Either way you must also be invited to apply after submitting an Expression of Interest, pass the points test, have a suitable skills assessment, and nominate an occupation on the relevant list. The nomination or family sponsorship is what makes you eligible to be considered for this regional visa.