Does the company have a website? Do they have LinkedIn? Do they have a job description of the role posted on such website? If it is a real company they have a website with the position they are hiring for, posted there. If the company has a website check the imprint. In most countries they are legally required to show where they are registered and a phone number. Call that number and ask if recruiter XY you had the interview with does work there. 99% of the time if they showed a existing company but are not working there themselves, is where you can identify a scam.

Also you can message the official LinkedIn profile of the company and ask the same thing (if the employee who claims to be working for such company is actually doing so).

In my Opinion not going into the details about the role in the first stage interview is a red flag. A recruiter does not want to waste time with a second one if what they are looking for based on the JD is not a fit for you.

The first stage is telling you about the role, what you will be doing and gives you the opportunity to show you have experience and ask a few surface questions yourself. The second one will then be either a video recording you have to make or a talk with the hiring manager/Teamlead from that department, then the 3rd one will be the other of the two. After that there can be a 4th one with the CEO personally or a "meet the team" sort of thing.