You should read up on Yanis Varoufakis' history and just how bad his solution for Greece went. That will explain the extreme amounts of anger on both his side, the side of Greeks and the side of the EU and worldwide financial community (and the EU itself used to be an industry cartel, so you can guess how much every government institution in the EU aligns with the worldwide financial community). This guy will never be allowed to do anything remotely serious in economics ever again, and he knows it very well. His Diem24 project is failing, and he knows that too. He feels the ECB, specifically Mario Draghi, Jeroen Dijsselbloem and Christine Lagarde are responsible for this downfall and talks about them in a way that makes you say "he can't be allowed near them. Seriously. Call the police". But in the constant tragedy of his life: He's probably right they caused his downfall.
He caused a MAJOR issue for Greece that still affects everyone in his country today, after reassuring people for 2+ years it was never going to happen: https://en.wikipedia.org/wiki/Greek_government-debt_crisis
(He'd kill me for saying this but he was lying back then too. He was trying to pull a Thatcher (I could compare him to someone else that did the same a long time ago but ... let's just say if you know you know). He was trying to double Greece's public debt by lying to everyone about what he was doing. He failed, and then started threatening, and when his threats didn't work, he got fired by Greece's prime minister, his oldest friend. It ended the friendship. He lost. And he's not a good enough sport to accept that he lost, frankly he got caught and couldn't talk his way out of it. This, despite the fact that he was finance minister, and so will be paid, very well I might add, for the rest of his life despite what he did, and despite the fact that every Greek today is still paying the price for what he did)
Oh and he's pro-Russia. All Russia wants in Ukraine, according to Yanis, is help the European poor. More detailed he is of the opinion that the current course of action of the EU will lead to a war with Russia, in which a lot of European poor will be forced to fight in an actual war, facing bullets and bombs in trenches. This could be avoided by giving Ukraine and the Baltics to Russia. In the repeating tragedy of Yanis Varoufakis' life, I have to say, yet again: he may be right (I just strongly disagree that offering Ukraine and the Baltics up to Russia is an acceptable solution to this problem, and in any case, this is neither his, nor my choice to make)
He does not live in Greece, his own country, he lives in the UK, making the case for Russia.
https://www.yanisvaroufakis.eu/category/ukraine/
And I get it, his life has become this recurring tragedy. His father was a victim of a rightist dictatorship in Greece, and he was imprisoned and tortured for that, as well as losing his job, living in poverty for a very long time (yes, Greece was an extreme right dictatorship not that long ago, really, go look it up). Yanis Varoufakis himself became the victim of a cabal of laissez-faire very, very rich people who destroyed his career right at the peak of everything he achieved. He has been the victim of one or another form of extreme-right policy (in the sense of laissez-faire parties that capture governments) since he was 4 years old, right up to today. Over 60 years his life was sabotaged in 1000 different ways, some very direct. And, sadly, I agree with his "extreme-right" enemies: he can never be in allowed near any position of power ever again because of this, which isn't even his fault. (extreme-right according to him, I would refer to his enemies as "the status quo", and point out it's working pretty well for everyone)