Before you play the file, use (free tool) to inspect the MKV. Look for these three lines:
: Excellent for finding movie trailers and audio/video format trailers specifically mastered in 4K HDR with surround sound. What to Look for in a "Best" Sample
A massive library of short, high-bitrate HDR10 and Dolby Vision clips.
Maya’s living room. A new 4K HDR TV is mounted on the wall. Leo stands in front of it, looking confused.
: Use a high-speed USB 3.0 drive or a local media server (like Plex) to avoid buffering. Playing these files directly via a TV's built-in player is often more reliable for triggering HDR than using an external laptop via HDMI. Samples - Official Kodi Wiki