I think it's ENTSO-E, here's their most recent report into an incident on 21 June 2024: https://www.entsoe.eu/publications/system-operations-reports...

For that incident, an expert panel was set up in July, the interim report was published in November, and the final report in Feburary 2025: so it'll take a few months.

I would expect the Spanish parliament to have some means of summoning an explanation, via its local regulator and grid authority. https://www.ree.es/en/about-us/regulatory-framework

Not required, but engineers tend to enjoy this sort of thing. Also, since it affected some 60 million people and EU-wide grid interconnects, someone will have to explain what happened.