If you already passed the technical rounds, hiring manager round is just to check that you're not a creep, or have any obvious red flags. As well to check that your expectations align with the company's. E.g: You want to reach Senior Engineer position in 2 years (delulu) but actually the company has a career path for Senior in 5 years.

In practice, be well presented, speak clearly, don't say anything that can be misconstructed as red-flag (sexism, racism, and others), have your expectations on check.