Cell phone setting samsung galaxy s10?

A friend of mine recently got the samsung galaxy s10 and if you just look at it from the side it looks like the screen is completely black (except for a small circle in the bottom center). It is only bright when you look directly at it. This means that people can't look into your cell phone as quickly. Where can you find this setting and is there this function also with Huawei (Huawei p30 pro)?

That's due to the display, which doesn't seem to be a good thing for your girlfriend

But you can switch it off again. I think that's an extra function.