Re: Resolution with Miracast
try to connect miracast to your windows 10 laptop or tablet that support miracast, setting the resolution to the highest normally would be 1080P or 720P, then disconnect from the laptop or tablet. try that on your phone again.
I had that issue to my samsung built-in miracast, and that is how i fix it. the TV is native 1080P, but the built-in miracast only support 720P max, but if I use the MS wirelss display adaptor, it works 1080P. So I assume your TV might be in similar situation