It's not quite perfect but at a fraction of the price of the HDFury boxes I've settled for this HDMI splitter XOLORspace Splitter downcaler simultaneously supports
I've got 4k and HDR10 from a Virgin Media set top box working fine.
What doesn't work is Dolby Vision or HLG so I find that, for example,the Netflix and Prime Video Apps on the set top box default to HDR10 for their HDR content instead of offering Dolby Vision and any HLG channels (BT Sport Ultimate and Virgin TV Ultra HD are the only ones I have access to) show on my TV in 4k but without HDR. For me, for now, that's a decent enough compromise as HLG content is in short supply in the UK and I'm willing to use HDR10 instead of Dolby Vision if it means my ambilight setup 'just works' and gets the wife's approval rather than having to mess on with different settings on a regular basis.
If I ever particularly want to watch something using HLG or use Dolby Vision rather than HDR10 there's meant to be a button on the splitter I can push to stop the output to my RPi which then allows HLG or Dolby Vision to my TV but removing the HDMI cable going to the RPi works too.