I just checked Amazon prime video's "stats for nerds" as instructed here , and the video is indeed running in FHD. It was just me being stupid and anxious as usual.
Thank you everyone for your helpful insights.
You haven't told us what kind of TV you have. The brand and model number would probably be helpful.
It's a well known fact that android ui runs on low resolution. It's almost the same on all tv. On 1080p tv it runs on 720p and on 4k it runs on 1080p
I updated the YouTube app and now the viewport shows 1280x720 * 1.5, so that's FHD and running on PC it renders 1920x1080 without scaling so I think the Panel is definitely FHD.
But I'm still not able get FHD video in prime video I tested the bandwidth on fast.com, its above 80mbps so that shouldn't be the problem, widewine L1 support is also present.
I also have vu tv full hd it shows 1280x720 I think the android ui runs on low resolution even I got confused
Cable, it's always the cable.
Most Android TV (including 4k ones) renders the UI in a lower resolution, but any properly optimized app will play video at native resolution.
You can easily see this effect in YouTube by turning on the "stats for nerds".
Android TV 12 will finally get the UI in 4k .