The old pc I used to download the rar’s is way too slow to playback the 1080p mkv. I’m betting the 2013 macbook air could do it, although I’m open to advice as to which video player to use (vlc, quicktime, etc).
I personally use both MPV and IINA, which is a Mac-only media player. I like IINA’s interface better but they’re both good. I’ve played the full 4K version on my iMac without any issues. Hope that helps. 😃