Grainy picture low light.

Hi guys,
I know, it‘s not necessarily a infuse topic but maybe some of you have a tip on that.

My setup: atv4. LG55c7. Streaming from my Mac via Infuse or directly via the LG-video app or Netflix or YouTube with the LG-apps.

I‘m seeing a lot of really very „grainy background“ when the scenes are a little dim. Watching the same movie in HD this is not visible.
I know that 4K reveals such imperfections. But I hoped, that for example in 4K Netflix series or the 4K Planet earth II. series the picture would be perfect.

I tried different settings on the tv and the atv (hdr Dolby Vision or sdr). My bandwidth is up to 92 mbps.

Does anyone have a clou what to do ?

Thanks for your help.