Looks like it's a thing from 15-20 years ago. I've never come across this license in any project; so it doesn't look like it is widely used. It looks to me like this failed to get a lot of usage.
I was in an EU project around 2007-2008 via Nokia Research. No mention of this license. But at the time they did have a list of licenses that were OK for licensing software. License like GPL, Apache 2.0, etc.
I do not wish to diminish Javier Casares's effort here: but it is nonetheless the case that a system administrator's WWW site about the EUPL is not the primary controlling factor when it comes to adoption of the EUPL, any more than https://www.pastafarismo.es wholly determines the popularity of Pastafarianism. (-:
I was in an EU project around 2007-2008 via Nokia Research. No mention of this license. But at the time they did have a list of licenses that were OK for licensing software. License like GPL, Apache 2.0, etc.