"From 2020, all scientific publications on the results of publicly funded research must be freely available." is not "All European scientific articles". I've got at least three papers that wouldn't fall under that heading.
It's a matter of perspective. I'd argue most European research falls under this. If you work at a public university and are paid for it and do research during that time and publish it that should be covered. It would be pretty lame if only stuff that was explicitly funded in a research project would be covered.
For example, if your position is at a public university, but funded by an endowment from a private foundation, is it covered?