1080p 10bit h265 can be played with the mi box easily. I know this since plex direct plays that format to mine.

4k 10bit h265 most likely you need a shield.

Smooth playback of video content means a device Must support auto Frame Rate Matching to sync the TV's refresh rate to that of the source video.

The cheapest combo for that is the MECOOL Pro W running LibreELEC Kodi Krypton from an external microSDHC card. It will easily handle 1080p 10bit h.265, even 24p 4K h.265

Get the Pro W with the USB mini receiver dongle wireless remote.

Otherwise you are looking at a NVIDIA Shield that does Plex, Emby and Kodi auto Frame Rate Matching. It's the only Android TV device that can do that.