To play Matroska video containers ( .mkv ) encoded with High Efficiency Video Coding (HEVC / H.265) on Linux Mint, you must ensure that your system has the proper media decoding libraries installed. The .mkv format is a flexible file container, but the underlying to render the video track.
Many media applications on Linux Mint use the GStreamer multimedia framework. To enable HEVC playback in these applications, you can install the libde265 GStreamer plugin. install hevc codec for mkv video on linux mint link
If high-resolution videos (like 4K HEVC) are lagging, go to VLC Preferences > Input / Codecs and ensure Hardware-accelerated decoding is set to "Automatic" or "VA-API". GStreamer Support: To play Matroska video containers (