To understand why the "GBA ROM" is a myth, we need to look at gaming hardware history.

If you are actually looking for the (on its original DS engine) with added features, Pokémon HeartGold Generations is a top-tier hack.

: A high-feature hack that includes over 835 Pokémon from across all 9 generations, Mega Evolution , and adjustable level caps to prevent over-leveling.

While there is no official GBA version of Pokémon HeartGold

Released in 2009 for the Nintendo DS, Pokémon Heart Gold is a beloved game that still holds a special place in the hearts of many Pokémon fans. However, not everyone had access to a Nintendo DS or a copy of the game. That's where the GBA ROM (Game Boy Advance Read-Only Memory) comes in – a pirated version of the game that allowed players to experience the Johto region on their Game Boy Advance.

Following Pokémon, a toggleable Physical/Special split, and a full day/night system. Customization:

These ROM hacks often provide a "best of both worlds" experience, combining nostalgic GBA graphics with modern gameplay improvements found on Pokémon Database : The HeartGold / SoulSilver Experience | Peak Remakes