MKV is just the container though, what really matter are the codecs and their parameters. Transforming the container (aka remuxing) doesn’t require a lot of processing power, and in fact some platforms like Plex will remux an MKV to another format on-the-fly to another container if the player doesn’t natively support MKV but otherwise support the codecs used inside with little effort required.
EDIT: I still don’t understand the general dislike towards Usenet in this community. Once I took the plunge, I honestly couldn’t dream of going back to torrents again. It’s just so damn convenient and reliable.
You can download in whatever format is available for any given movie. Often movies are available in multiple formats, especially the popular ones. DM your email address amd I can invite you to a private tracker but only if you promise to keep a good ratio.
Also I’m sure some other commenter is literally going to say “mkv is a container not a format” but whatever, if you want mkvs the movie or show you want has to have an mkv available.