What are those categories within a category for a game? Like Minecraft for example, under Any% Glitchless, there's Set Seed and Random Seed, etc. so how do I make those categories for the game I moderate?

Edit Game -> Variables -> New variable -> name your variable -> New value(s) -> name your values -> click the 3 dots next to "New value" -> Edit variable -> click on "Use as sub-category" -> apply proper Level and Category -> Save

If you're adding sub-categories to already existing runs, make sure to click on "Set the default for all runs without a value."

Sr.c have their own page on editing a leaderboard