Option 1: Use "Cast desktop" function in Chrome browser ( https://www.lifewire.com/use-chromecast-to-show-windows-desktop-4129536 ).

Option 2: Install a remote desktop client app on your Mi Box. In particular, Microsoft Remote Desktop ( https://play.google.com/store/apps/details?id=com.microsoft.rdc.android ) is really fast if your internet connections are strong on both ends. As a test, I was able to watch videos stored on an office computer this way with very little stuttering. Since your computer and Mi Box are in the same network, this shouldn't be a big issue. The only thing is Microsoft Remote Desktop is not officially supported on Android TV even though it works well. You'll have to sideload it (e.g. Aptoide). There are other remote desktop apps in play store but their speed & image quality may vary.

Option 3: Use Steam Link app ( https://lifehacker.com/use-steam-to-stream-your-desktop-instead-of-your-games-1818722875 ).

Option 1 is simpler if your computer and TV are close. Option 2 & 3 work better if there is some distance between them and you don't want to walk back and forth.

I answered below then realized I wasn't sure what you meant - do you have local media you want to play? So you need to know what program will cast? Or you want to remote in and view your win10 screen on your tv?