There was an update to the Wikipedia article on May 8, 2023 by User:Virtuus.
Sharing the text of the edit (emphasis mine)
the France24 article about the Greek church has a typo. According to this Guardian article: https://www.theguardian.com/world/2011/oct/04/greece-orthodox-church-economic-crisis, the [sic] "the church was worth €700m in 2008", not "€700 billion"
The Guardian article in question, "Orthodox church appears to be exempt from austerity measures" (Alain Salles, 4 Oct 2011) quotes the net worth at €700m, or possibly up to €1bn, and provides additional context:
According to the right-of-centre daily Kathimerini newspaper, the church was worth €700m in 2008. Manos, a former finance minister, reckons the figure is at least €1bn. The €2.5m in tax paid is slight in comparison to these unconfirmed figures. But this is only part of what the church owns, in the care of the central administration. It does not take into account the many parishes, some of which are very rich, nor property under the direct ownership of Greece's 80 bishoprics, which enjoy considerable independence. It also overlooks the wealth of 450 monasteries, some of which are affiliated to the church, others not (those on Mount Athos, for example, have a separate status). The Orthodox Patriarchs of Constantinople, Jerusalem and Alexandria all own property in Greece. "Greece is staring at a pile of money and everyone is behaving as if it was invisible," says author Vassilis Alexakis, who has written a caustic novel about Mount Athos in French.
While this does not directly answer the question of what the church is worth today, based on this inflation calculator, €1bn is worth about €1.4bn in 2024, over two orders of magnitude less than the €700bn quoted.
The France24 article (27 June 2011) does not appear to provide a source for its claim.
Based on the evidence from the Guardian article, we can rate the claims as follows:
Is the net worth of the Greek Orthodox church around 700B Euros?
No, not in 2008 Euros and likely not today. And,
Is the Greek Orthodox church the single wealthiest religious organization in the world?
No, as 1.4B Euro is less than other organizations listed including for example the Church of England (quoted at 12B USD = 11 Euro), the Catholic Church in Germany (quoted at 26B USD = 24B Euro), and the Mormon (LDS) Church in the United States (quoted at 236B USD = 220B Euro).