Fast Forward - NDS

I'm trying to play Pokemon Platinum on my Steam Deck. However, the speed of the game is abysmal, even with Fast Forward on.

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I tried everything I know, even trying Desktop mode. The maximum I got was 300 FPS registering on the core Melon DS, but it barely looked like it accelerate even 2x more. I tried all cores from RetroArch, MelonDS, desktop mode, gaming, turned off frame limit.

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Is Platinum in the DS hopeless slow or are there anything else I could try?