How do I get a full screen with Huawei Smartphone?

In the YouTube app, the extra screen space is not used!

If you tap on the video for a moment, you'll see additional options such as pause, rewind, … In the lower right corner there should be a rectangle, you have to press on it.

If you mean the full-image mode then you can zoom with two flingers, that is the notch also "enclosed"

No Bro I mean like in the picture already to see that with the comments because the surface next to Notch is not used above the video looks just a bit smaller from the screen. If I'm on the YT homepage or anywhere in the app, the surface is used but not if I want to watch a video while reading comments

If you mean the notification bar, you can't change it. This is due to YouTube and there's no hiring for.

So there's not this software option?

Yes man, I mean the notification bar.