Let me quote rule 1. : "Submissions must be a fully playable RPG system on a single page".
The allowing of second side and character sheets (and other stuff) should have to be not needed for full playfulness.
FAQ answer; The game can be spread across both sides, but keep the core rules onto a single side. Use the 'back page' for ancillary info such as GM tools. https://itch.io/jam/one-page-rpg-jam-2024/topic/3889509/faq-2024