Is he a good economist, though?

I mean, I can write books and host radio shows about quantum mechanics if I want. And I'm no physicist.

But regardless, if he's a climate denier, that's all I need to know.

I'd say I'm more afraid he's also a talented enterpeneur for a product of his speeches and personality. I've met some people called visionaires, and I'm sure he may be one of these. They are not necessary bad in their field, but their word is taken for granted in too many indisciplinary cases and they are succesful at selling it at many conferences worldwide. He may be a really talented economist, or a man that just have an instinct to getting a career here, it doesn't matter. That characteristics just makes him more likely to succeed at elections, winning the public.

More important to my judgement of him is that he uses a populistic platform of redoing everything from the ground up in an instance. I get people got fed up with previous governments, but nothing good happens overnight. It's a big red flag. Even if he's trully the savanth scientist who planned it all himself for 20 years and get it all perfectly right, the amount of changes themselves would cause a crisis. And him accepting it, not seeing it or serving some lobby makes him not a president material equally.

I didn't say they can't, I said it was fraught. A better phrasing is "can cause issues a non-euro country does not have." This quote explains what I mean:

So, in the eurozone a national (federal) government cannot run out of money as long as:

• tax revenues are high enough to bring the Treasury account back to zero or
• bond revenues are high enough to bring the Treasury account back to zero or
• tax and bond revenues together are high enough to bring the Treasury account back to zero.

This means that a eurozone national government does not run out of money until it has exhausted its tax revenues and bond revenues

The United States, Great Britain, Japan, and every other fiat currency country don't have this problem. They are incapable of running out of money. They are capable of making so much money it is completely debased like Weighmar Germany or Zimbabwe. However, those cases are rare and extreme. As long as they ensure the supply of goods people want to buy us sufficient they can spend as much as they want. This enables them to pay off their debts on a whim (if they want to collapse the safest store for money that investors use to outweigh risks).

Sources:

The Deficit Myth I'd give you page numbers but I listened to the audiobook https://www.intereconomics.eu/contents/year/2022/number/2/article/modern-monetary-theory-the-right-compass-for-decision-making.html

He literally said it's the MMT. Lmgtfy: https://www.investopedia.com/modern-monetary-theory-mmt-4588060 and it doesn't even say that companies can't get loans.

It just makes it harder to take on debt if you don't control your own currency as a sovereign state. EU countries are a political union but not a clear fiscal union, with their own treasuries but also the ECB calling the shots and it means that member states can have sanctions imposed on them, like Greece for example.