According to [1], what happened was that volunteers were recognised as workers by ECJ and as such their time on call at home can count towards their weekly worked time. An older directive (2003) sets out a maximum working time which I am sure nobody is complaining about, and if anything in many member states people claim to be working to many hours. Individuals can and could previously opt-out of these limits. Nothing new under the sun here.

It is also clear that no "regultation" is being planned.

[1] https://www.europarl.europa.eu/doceo/document/E-8-2019-00020...