Hello Makhno95,

Thanks for using Apple Support Communities. 

I understand that while watching a QuickTime video in full screen, the mouse pointer and playback controls are still appearing. I use QuickTime to watch many videos, so I know it's important we get this resolved. I have a couple of things for you to try. 

First, it's important to make sure that your mouse pointer is not on the playback control menu, and it is positioned to the far-left or far-right of the QuickTime video you're viewing.

Next, I would suggest using the QuickTime Player Help guide and trying this in different screen sizes, specifically, this section: 

Choose a screen size

You can set a movie to play at the size that best fits how you want to watch it.

 

• After you open the movie, choose a size option from the View menu:

   
   
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    Enter Full Screen: The movie is displayed as large as possible and the menu bars are not visible. To exit full-screen view, press Escape.

      

    You can also click the Full Screen button in the upper-left corner to enter full-screen view. To leave full-screen view, move the pointer to the upper-left corner of the screen, then click the Exit Full Screen button . For more information, see Focus on apps in full screen or Split View.

     
   
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    Actual Size: The movie is displayed at its source size.

     
   
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    Fit to Screen: The movie is scaled to fit your screen.

     
   
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    Fill Screen (only in full-screen view): The movie is scaled and cropped to completely fill your screen in at least one dimension. This can eliminate black areas on the top (letter boxing) or side (pillar boxing), but may hide or distort the content.

     
   
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    Panoramic (only in full-screen view): The movie is scaled to fit your screen, and the outer horizontal edges are compressed to avoid cropping the image.

     

Best Regards.