Bragg doesn't have jurisdiction here. He can't say "This guy broke this law" when it's not on him to prosecute that.

Sure he can. There were several cases cited in the judge’s ruling where that exact thing happened - a person was convicted under the business records law for attempting to conceal a federal crime. Bragg can’t prosecute it, but he can prove it up as an element of the state law case. The law is crystal clear on that - the prosecution had several NY cases on that point, the defense had none, which is why the defense lost the ruling.

So did the IRS weigh in on this? Why wasn't this tried in federal court also?

State tax filings. Cohen filed fraudulent state returns. The IRS has nothing to do with it.

How is this a felony?

Because that’s what the criminal statute says. If you falsify business records with intent to conceal another crime, it becomes a felony. The “other crime” doesn’t have to be a felony.

The judge barred the former Election Commissioner guy from testifying that what Trump did wasn't even a crime under federal election law. How can a judge say a witness can't testify "because it might confuse the jury"?

Because witnesses aren’t allowed to “testify” as to matters of law. It’s up to the judge to determine what the law is, including whether a set of facts (if proven) would violate the law. That’s why the defense was told they were perfectly free to call him, but he couldn’t propound on legal issues - just facts. Which is what witnesses are allowed to do - testify on factual, not legal, questions.