You enter in the ID of a game. The ID for Minecraft: Java Edition is "mc", so you put that in the box. If you want category extensions, you put in "mcce"
You can find the ID of a game by looking at the URL, and it should be the one next to the first slash
This is a unique release, as no rule changes were made. This release should be functionally identical to rules v4, with only minor whitespace and formatting changes.