I think it has been known for a good while that Amazon Prime Video is SD only on system running anything other than Windows and MAC: https://www.primevideo.com/help?nodeId=GUX9FYHU5D8LC9EJ
Is there a way to work around this limit? It'd be a shame having to use a virtual machine running Windows (if it even works) to just watch Prime video.
According to this forum, the following solution might work:
1) Install
winehq-staging
2) Install Edge-dev: see this
3) Run Edge:
wine 'C:\Program Files (x86)\Microsoft\Edge Dev\Application\msedge.exe'
4) Log in to amazon prime video using your newly installed MS Edge browser and HD could work
Let me know if this works....