Valid OPT JOB OFFER?

Hi everyone, I just graduated in December and applied for the OPT in November. My start date will be February 10, 2025. However, I have not received any job offers. Fortunately, my mother's friend has a company (which includes a nail salon and a restaurant) in South Carolina. I just asked her to allow me to work as a volunteer data analyst at her company (my major is Computer Science.) My question is whether I can do it and if I do, whether this job is valid so that I can report it to my DSO and the SEVP portal to avoid 90 unemployment dates. Thanks