HDR on Win 10 is still a mess, right now I just wouldn't bother building a media machine on a Ryzen APU (or anything else) for use with HDR.
I've been through several AM4 ITX motherboards, ASRock, Gigabyte and MSI, none of them handle HDR with a Ryzen APU on a 4K HDR TV
The ASRock didn't even work properly at 4k 60hz (RMA'd one board thinking it was a fault and the the replacement did exactly the same thing)
I've tried several APU's to eliminate that, multiple ram kits.
I'm currently using the Gigabyte B450-I-AORUS-PRO.
It works fine running an LG OLED TV at 4k 60hz (HDR is a mess)
If you want HDR that just works, get an Nvidia Shield tv or just use the apps on the TV you buy for Netflix etc.
https://www.nvidia.com/en-gb/shield/shield-tv/
Or just build the Ryzen system for light gaming and 4k 60hz playback and forget about HDR (for now)
You could also investigate an Intel system using Kaby Lake (or newer) CPU and a low end Nvidia card (such as a GTX 1050)
I just got so fed up with HDR on Win 10, I've completely given up on it until it works properly !!!!
