[NackteElfe]

PS:
Might the reason I cannot run 4k be that I am using display port instead of HDMI to connect my screen to my PC?
I don't have a decent HDMI cable lying around, otherwise I'd test it out myself.

Also: Can someome tell me if I should enable the HEVC profiles or not on a Windows machine. It would be me help to corner in the problem.

Looking at the resolution feedback on the first page, I see nothing about Windows and 4K playback, so maybe it's not currently supported as yet. I haven't tried using any of the beta versions myself, so can't confirm, but my gut feeling is probably not.
You will also need a PC and Display that are both capable of 4K playback. I would also recommend using a HDMI 2.0 cable. 

Yeah, it really looks like Kodi is not ready for 4k Netflix (or Prime Video in that matter).
I did intensive research and it looks bleak. I even got the most expensive HDMI 2.0b cable that I could find, without getting better results (so I switched back to display port, because it suits my needs better.)

PC and Display are capable of 4k, of course. Using the Netflix App or Edge I can watch 4k content, also 4k Youtube and other 4k Videos are playing just fine in Kodi.
It really seems to the plugin that is not ready for (Windows) 4k (yet).