He donated the same amount to the GOP it's not getting as much attention.

That is probably because the source on his dark money donations is SBF and that's it.

What does he have to gain out of saying that?

My only take is that he can prevent prevent Fox & hard right from further making him to be a democratic super donor and try and paint the entire democratic party/system as corrupt.

SBF has claimed to have donated as much (without proof), but he's also claimed to have not committed any crimes.

What would he have to gain from lying about donating to Republicans? He lies about not committing crimes to stay out of prison.

Seems like a lot of partisans want SBF to be a democratic cartoon villain and won't let reality get in the way of that assessment.

He's been very careful and cagey about those other claims though - things like saying he didn't implement an FTX/Alameda backdoor (deliberately avoiding the more important issue of whether one existed and whether he used it) and saying he didn't try to commit fraud (sure he didn't try, but he succeeded on a rather impressive scale).