After comparing several of these directories, seems https://euro-stack.com/ is the most comprehensive. I also like that it allows to filter by both being European and open source.
It is also made by the same people who run https://eurostack.eu/ and who got a lot of visibility delivering the https://euro-stackletter.eu/ letter to President Von der Leyen a year ago. Hopefully they settle soon on what is their primary domain :)
It’s if the project is of european origin or the leading mantainer is european