Netflix app jerks during playback?

With me on my cell phone (Samsung Galaxy S20 Ultra), my Netflix jerks extremely as soon as I start playback.

In general, my cell phone is extremely slow.

What could be the reason?

No memory, slow internet, your mobile phone has to perform too many functions at the same time

So I still have about 100GB of free space and my internet is actually pretty fast. Because I can stream 4k fluently on my Smart TV.