Well, the reports coming in suggest this issue is now fixed. It took a year but Dell finally got it sorted. So I think I'm happy to mark this problem as resolved.Thanks to everyone that contributed to this thread and I'm glad the laptops can finally do what they were meant to be able to do.  
I have the Dell XPS 15 9500 4k and have been having issues with streaming 4k video. Basic spec:9500 4k Touch ScreenIntel 10750H16 GB RAM1650 TIThe Problem:The laptop is now unable to stream 4k from Netflix/Disney Plus. 4k YouTube video very jerky and unwatchable.I want to see if anyone else has this problem and go over what Dell has done so far. This is our 4th XPS 15 Laptop we bought for work (this is the only 4k model though). Really like them so this isn’t a “slag off Dell” post. Just wanted to write up where I am with it. Sorry for the long post. When new (bought in late 2021), this laptop played Netflix 4k films fine using the Netflix app. When you go into Netflix and select a film (say 6 Underground), the info shows its Dolby Vision - Atmos. It played the film in full 4k, HDR etc. This can be checked by pressing CTR, SHIFT, ALT, Q when the film is running to pull up the nerd info from Netflix. Here it shows it’s running in 4k etc. Disney Plus app also worked fine in 4k. Using Edge browser to open Youtube and run a 4k 60 FPS video was also fine. Stats for nerds showed no dropped frames here, great video smooth playback. A couple of months on I’m not able to play 4k films in the Netflix app, get Netflix Error U7361-1255-8004CD22. Select the film and the info shows its Dolby Vision – Atmos so it should be able to run in 4k but won’t.YouTube will play the same 4k 60 FPS video but it's jerky and unwatchable, stats for nerds show its dropping frames constantly. The only thing that’s changed on the laptop is updating the windows updates and the Dell driver updates. As of writing, ALL bios, driver, windows updates are done. The Intel Graphics Command Centre says the display is NOT HDCP compatible. I’ve spoken to Dell, they confirmed the machine is HDCP 2.2 complaint. They thought the motherboard was faulty so sent a tech round to replace it. We replaced the mobo and put in the same Hard Drive and booted it up. Netflix was now able to run a 4k film, but it was jerky, out of sync with the sound and basically unwatchable. YouTube 4k test video was just as bad as it was before. The Intel Graphics Command Centre still says the display is not HDCP compatible.The Dell Support software found a new bios update for the motherboard, so we flash the bios and install it. Reboot the laptop and now Netflix and Disney Plus won’t play the 4k movies. They throw up the same error codes that mean there’s a problem with HDCP (Disney Plus is error code 39 I think)I decided to do a full Windows restore and wipe the computer and reinstall windows 11. Fresh install with all the relevant updates and the same problems. Same error codes on Netflix and Disney Plus. Same problem on Youtube 4k video playback. Dell has offered to replace the laptop but as the 9500 is no longer made, they offered the newer 9510. The problem is they don’t have the 4k screen model so was only able to offer the basic entry model. Whilst I appreciate this, I do need the 4k so as of now I’m waiting for that to become available but it's looking like it will be months before a replacement is offered.I would be happy to keep my current laptop if there was a way to fix it but as of now, we can't seem to do that. Does anyone else have this issue or do just have a faulty laptop that needs replacing?
XPS 15 9500 4k Video Playback Problems