I have noticed that some games link their Category Extensions board to the main board and Vise Versa. Can someone explain how to do this?

They have the Category Extension game type, with the base game set as their main leaderboard.

To get this updated, you need to submit a support ticket. Link: https://www.speedrun.com/support/tickets/new

On that page, select "Change an existing game or series", and then "Change the type of an existing game". Then select your Category Extension board for the game, tick the Category Extension game type check box, and set the base game to your main leaderboard.

Thanks

Also I see that your CE board was added recently. https://www.speedrun.com/_Indigo_Park_Chapter_1_Category_Extensions

Bruh @starsmiley, how'd this get added without the correct settings lmao

Is it my fault it was setup wrong?

No, just normally category extentions do have the correct settings.