Today my beamer arrived (https://www.amazon.de/Tragbarer-Unterst%C3%BCtzt-Videobeamer-Kompatibel-Chromecast/dp/B07HQQPY8C/ I connected it to my laptop with HDMI (Predator Helios 300). My drivers are up to date and my laptop's performance should not be so. Youtube works perfectly. When I open Netflix, it works too. When I then play a video on Netflix, it is as if every 1.5-2 seconds would be missing 1 or 2 frames. If I pause Netflix, it's still like that. Only when I close the tab with Netflix, everything goes again. The same with Prime Video.
Update: With the Netflix app for Win10 it runs without problems. With Netflix in the browser in the information (Ctrl + Shift + Alt + D) there's always something between 3-5 in Current Dropped Frames. In the app there's always 0. It will probably be, if someone has an idea to fix it.
So if someone has the same problem: it's simply Google Chrome. There are no problems with Microsoft Edge. Is at least the case with me.