Two interviews with two different employees. I had to do a practice for the job, an hour of test questions about the role and talk about it with the senior employees

The hiring manager was not inviting or welcoming at all and she would not disclose salary and visa sponsorship questions. These fields are mandatory when it comes to employment. The answers received were very vague and later on I understood that this is an unpaid internship. How is this legal? I would never recommend to people to apply to unpaid internships regardless of their level of expertise/education.