HDR does, with 600kbps download, TV even has HDR activated when something is specifically HDR and 1080P works perfectlyHDR defo dosn't work at 6mbit nor does 4k, i'm a bit surprised that 1080p does to be honest.
Maybe you should have a look at this, Amazon's own website with the recommended download minimum speeds for all formats:
https://www.amazon.co.uk/gp/help/customer/display.html?nodeId=201648150
As you can see, at 600Kpbs you would be lucky to stream anything. In an earlier post you said you have a 6mbit connection, good enough for 1080p but nowhere near enough for the 15Mbps needed for 4k HDR