I recently got my request of adding Eli on to this site approved. Now, Eli has 3 gamemodes: Normal, Hard, and Hyper. Now, I remember going on the Super Mario Oddysey any% leaderboard and seeing this tab on it to choose between 1P (1 player) and 2P (2 Player) how do I do that so then there will be 3 categories within Eli any%?

You can add tabs in the Variables area.

Thanks

More specifically, you need to create a variable and set it as sub-category.
You can find useful information about leaderboards configuration here: https://www.speedrun.com/the_site/thread/pgxyw