Okay, first off, let me give you some basics:
The way most discs works is that they have something called a “disc image” written on them. This is resembled as an .iso file when you are working on a computer. It is inside this .iso file that the instructions for reading the disc are located.
Now, there are different types of encoding for DVD’s and Blu-Rays. DVD’s have an AUDIO_TS and a VIDEO_TS folders. Blu-Ray DVD’s have a much more complex file hierarchy. So, if you are wanting to burn to a Blu-Ray, you will not be using a VIDEO_TS folder. You will want to write to blu-ray if you have a file larger than 8gb and in HD.
Now, lets get to burning. Most Blu-Ray players nowadays have a file browsing system, meaning if you can plug a flash drive into the player, you can browse media that way. Now, if you just want to burn an .mkv file, you can do it simply by dragging and dropping the file onto the disc through Windows File Exploerer (if on Windows). However, it may not work the way you would expect when you put it in the player. Usually, if your player does have a file browsing system and your disc was not written with a .iso, it will require you to find the .mkv file on the disc and then play it manually. That means no autoplay, because the instructions for that don’t exist on the disc.
Now, you may just want to convert the .mkv to an .iso and then write that to the disc so that it does play more like an authored disc, however this can be a bit confusing, and I haven’t personally done it myself.
The Despecialized Editions and the 4K## Projects each have .iso files available, so if you want to avoid all the hassle I mentioned above, simply download the .iso versions instead of the .mkv. I would recommend this as the best course of action for writing to discs. The DEED .iso’s are actually fan projects, so they also come with disc menus and a bunch of special features.
Here is the page for Despecialized .iso files: https://originaltrilogy.com/topic/NJVC-Custom-Blu-ray-Set-of-Harmys-Despecialized-Editions-now-available-on-Mega/id/57042/page/1
This person can help you if any of the links are dead: https://originaltrilogy.com/user/SnooPac/id/21956
I hope this helps!