HDMI connecting at 4k 30Hz

I have an AMD RX 570 which is supposed to support HDMI 2.0b and three 4k monitors (one a brand new Dell) that support HDMI 2.0, and while I can get 4k@60Hz over displayport I am stuck at 30Hz over HDMI for all three monitors and both HDMI ports on the card as if they're connecting at HDMI 1.4. They run at 60Hz with Linux & they seemed to be running 4k@60Hz with 4:4:4 chroma subsampling not 4:2:0 according to some test image I downloaded from https://www.geeks3d.com/20141203/ho...-chroma-subsampling-used-with-your-4k-uhd-tv/
$ xrandr
HDMI-A-0 connected 3840x2160+7680+0 (normal left inverted right x axis y axis) 608mm x 345mm
   3840x2160     30.00*   25.00    24.00    29.97    23.98
The suggestions from this thread: Thread freebsd-and-hdmi-tv.79869/
sysctl sys.class.drm|grep HDMI
dmesg -a|grep drm
...didn't seem to give any useful info. It seems likely the graphics card is connecting at HDMI 1.4 speed, how could I check and/or override that? This is on 12.2.