Cannot Enable HDR on Settings

did you set colors to limited or full?

Use limited colour range (16-235)

please provide from ssh:

cat /sys/class/amhdmitx/amhdmitx0/config

see also this HDR not working properly after April Update (Vero 4K+) - #12 by nabsltd

also Sony X900E Calibration Settings - RTINGS.com for this:
In the ‘Video options’, just verify that ‘HDR mode’, ‘HDMI video range’ and ‘Color space’ are set to ‘Auto’ and it should change automatically to match the type of content you are watching, in this case, HDR content.