The complete explanation I use for MKV is "a bucket"
You can put almost any media into a MKV in almost any encoding.
Since this TV does not understand the encoding in the content that is in the MKV, it does not play. So be sure to understand that there is usually no issue with MKV support because that's just a bucket of content. Now that we know this we can understand that to play what's in the MKV we have to be sure the encoding is supported.
This means you, like thousands of others will have to either get the content in compatible files or learn how to re-encode the content on your PC or Apple computer.
About that CODEC. This HDTV is not a PC so there is no support to add such to the TV,