No HD or Full HD Streaming or Downloading for Prime Video by Amazon. Although Netflix have no issues. Device is Widevine L1 certified. Might be the issue with Prime Video technical team who are still working on the HD or Full HD features in the latest devices.

Tried clearing cache of the app, data of the app, uninstall, restart device, re-install. Still same issue. My budget Tab Samsung Galaxy Tab A 10.1 is having HD and Full HD. This new premium Tablet costs 4 times money and don't have HD or Full HD.

My device details
Name - Samsung Galaxy Tab S7 Plus
Model - SM-T975
Variant - 128 GB ROM & 6 GB RAM