For Trump, this charity was like opening up a bank account into which people could deposit tax-free bribes.
As far as I can tell, that isn't it. Trump's issue was that he was using the Fndn to make it look like he was charitable to increase his personal persona. I've read stories about him showing up to charity galas, getting his face in group pictures as if he donated at all. There is a wing of a hospital named after a Trump that was paid for by donations other people made at Trump hotels when signing off on their bill. The Trumps put some money into their own Fndn and made a few donations, but then pretty much just would take money in from other people, like the McMahons and use it to project Trump charity at best, not the McMahons.
Then Trump ended up using the Fndn to pay off court settlements, and even political campaigns, like the Attorney General in Florida (Pam Bondi)... who oddly enough stopped investigating the Trump University thing. So while that last one was a bribe, I believe he generally used his Fndn as a PR stunt, but stopped actually contributing to and used it for self promotion or lawsuit payoffs... which I'm pretty is why Linda McMahon has John Cena on standby to go kick Trump's ass when it is confirmed that McMahon money was used to pay off a stupid lawsuit over a fucking flag.