That’s where there should be a requirement to demonstrate that you have removed yourself from any conflicts of interest. Trump didn’t do that (at least not in a way that’s satisfactory to me), and I think there should be a change to the qualifications for President that includes some level of divestiture.
the president has the ability to crash the value of the American currency
But the President doesn’t really have the power to do that. The Federal Reserve does (and there’s a lot of legal barriers between the President and the Fed) and Congress does, but the President can’t directly crash the value of the dollar. Look at Trump’s campaign, he says he should have direct control over the Fed, not that he does. Making that change would be a big deal that would piss a lot of people off.
The Supreme Court immunity ruling is absolutely dangerous and Congress should fix that ASAP, but that doesn’t mean the President can go devalue the currency on their own. That’s just not how things work. The closest they can do is attempt to fire board members of the Federal Reserve and appoint new ones that would hopefully listen to them, and that would be challenged by the Supreme Court. According to the ruling, they’d be immune from making the attempt, but that doesn’t mean the attempt can just go through w/o review.