[rob_l12]

@Sukhish incorrect. This plugin fully supports HDR, 4k and Dolby Surround, but playback is limited by Amazon & Google. 4k in particular requires certified hardware, so if you're running Kodi on a Firestick for example, no problem, but if you're running it on a RPi or a PC, you won't even get FHD.

I think that Firestick counts as android, so you should enable Android playback method instead of InputStream.Adaptive. IS.A can't manage 4k/HDR due to DRM restrictions.

Don't want to sound pushy or anything (just trying to understand the technical reasoning behind it), but are you sure about that statement regarding IS.A?

Reason I ask is that on my Nvidia Shield I cannot get this plugin to play 4K HDR streams from Amazon, even though the Netflix addon that also uses IS.A is capable of doing this.

Now that Amazon has lifted the Covid-19 limitations and enabled 4k in their own app again, I was hoping the plugin would also play 4k streams through IS.A.

By the way, the option to play 4k using the native app doesn't work on my Shield either. Is there anything special I should do to get this working? 

I certainly don't have any problem playing 4k (even HDR) content on my Nvidia Shield through the standard app (I have the original Shield Pro, but that shouldn't make any difference). I'm assuming you're not one of those people who've chosen not to upgrade to the latest system version, but again I don't think that would make a difference in this case.
I'm in the UK FWIW.

Like you, I get 4k HDR with Netflix without an issue. I was pretty sure I used to get 4K playback within Kodi too, but I can only get FHD now. I fully expect Varstahl to tell me I imagined that, though :-)