You can own anything that it is legal for any American to own (except for guns and a few other restrictions). So you could definitely have ownership interest

You can own anything that it is legal for any American to own (except for guns and a few other restrictions). So you could definitely have ownership interest in the company. I would look for a better immigration lawyer - IME many of them are on the lower rungs of lawyerly proficiency to begin with and are dumb, fat, and happy as a result of collecting thousands of dollars to basically help you fill out paperwork. Finding one that already has experience helping someone with what you want to do is key.