What are these little flies/mosquitoes in the apartment?

According to my friend's description, there have been an incredible number of small flies in her apartment for the past two days. These are slightly larger than fruit flies. They are therefore not fruit flies. They are black. They are not food moths or anything like that.

They're all over the apartment and not concentrated in the bathroom or around drains. She poked around in the drains to see if they were coming out. They weren't.

They are mainly found in the upper part of the apartment or on the closet, especially on the ceiling.

She doesn't have any trash lying around the apartment, and she's thrown away crumbs, etc. But there haven't been any fewer of them; in fact, they've continued to multiply.

She doesn't want anyone (for now) to come and look at it and cost money.

What do you advise her? What could it be?

I didn't see it with my own eyes.