these are assets and companies in total (from 1983 to present), the majority of them are of cosa nostra

And that's only the local investments/assets, Italian organized crime is moving billions of euros abroad all around the world.

With all of that value seized, it still surprises me that they can still operate. Is there any accurate estimation on what they are worth based on asset seizures? They must be worth five times the assets that are seized in order to keep operating like business as usual.

I already said it multiple times , good % of that assets seized are returned back after tons of trials and so on. Also when state puts all that assets on public auction , everyone know who it belonged and people are afraid to buy it , its bought again by families/close associates of mafia , so it finds its way back to their hands again

Yes, although several mafiosi have complained about all the seizures on wiretaps, that's why they prefer to move money abroad investing in Romania, Germany, Spain, US, Canada etc..

Are there any South American criminal organizations that compare to the top orgs?

Probably Colombian

Clan del Golfo and Oficina de Envigado.

Other than Matteo Messina Denaro, what Sicilian mafia member had hundreds of millions of euros worth of assets seized? Stefano Bontade had money but I don’t know how much money we could really trace back to him.

The major bosses don't have millions stashed away they use legitimate people who control the assets. For them it's more about power than money.

That’s what happened with Denaro. Legitimate businessmen were tied to him. Multiple billionaires were accused of bankrolling him. Is it safe to say that only a portion of the assets seized were really Denaro’s then? Or is he totally responsible for the wealth that they amassed in the first place?

2021 updates? any changes

as of 2024 has this changed?

I would say the European and former Soviet/East-Asian syndicates have grown in recent years.
Mexicans ofcourse now also expanding in Europe, Colombians and other Latin American groups.

So many hotbeds in Europe alone from East (Balkans) to West (France, Benelux), From the South (Italy) to the North (Ireland, UK).

what is the single most powerful organization in all of Europe in your opinion?

'Ndrangheta, The 'Ndrangheta has existed for as long as the better-known Sicilian Cosa Nostra, but was only designated as a Mafia-type association in 2010 under Article 416 bis of the Italian penal code. Italy's highest court of last resort, the Supreme Court of Cassation, had ruled similarly in March 2010.