yes, like I said everything was fine with 4k hdr via Apple TV last week, I’ve just tried today and the same films don’t play 4K hdr anymore, even though they are the 4K und hdr versions. So the Apple TV has just started not playing them, and I didn’t know if this is/has happened to anyone else. (Could of been an automatic update to prime on Apple TV that has done this by mistake?) I don’t know. But it’s a bugger as I just watched knives out in just hd when they had the 4K uhd hdr version. (Just watch a bit of it on prime via the LG tv prime app, and it did look very nice).You should still be getting HDR10 via any device in association with the tytles inclusive of HDR. There are lots of HDR10+ titkes that you'd need both the source and your TV to support HDR10+ in order to get dynamic HDR10+, but even if you've not the compliant devices then you should still be getting static HDR10 in association with that content.
Find the 4K UHD encoded variants of the content is an issue with Amazon. THey make both a HD and a UHD version available, but don't make it easy to find the 4K versions if and when there is a 4K variant being hosted. Onlt the 4K UHD version will be inclusive of HDR. TRy searching specifically for the UHD 4K version.
RE; HDR via Amazon Prime via the Apple TV: You may find this of interest:
I'd therefore suggest that there is an issue accessing HDR via the Apple TV.