ASUS has specced out the ROG Strix XG438Q with some of the highest-end specs you could ask for: native 4K resolution so we have 3840 x 2160, joined with a super-slick and smooth 120Hz refresh rate. ASUS has included FreeSync 2 HDR support, but for 95% of my time with the display I had it powered with an MSI GeForce RTX 2080 Ti LIGHTNING Z graphics card -- I also used an NVIDIA TITAN RTX for some testing, and finally an AMD Radeon RX 5700 XT.
AMD FreeSync 2 HDR Support + DisplayHDR 600 Certification
ASUS includes Radeon FreeSync 2 HDR support, but this is something I really don't like -- HDR gaming in general. Windows 10's HDR implementation is absolutely shocking, so I don't even bother with it for the most part. Normal gaming however, is an absolute achievement in all senses of the word on the ROG Strix XG438Q.
Also, there's literally zero Radeon GPU hardware on the market that can handle a majority of games at 4K 120Hz... so you'd be reduced to playing games that don't tax the graphics card that hard at 4K to hit 120FPS in the first place.
But, if you did want to enable HDR then ASUS has your back with DisplayHDR 600 certification and DCI-P3 90% color gamut.