It's hard to evaluate the 500k statistic without knowing the total number of deaths in that period. Does that represent most of the deaths, or a small amount? A quick web search brought me to this page, which claims "Europe" had 9.6 million deaths in 2021. I put Europe in quotes because that is what the page says and the EU is not necessarily the same as Europe, especially as that graph goes back further than the EU. But it's probably a good rough estimate.
Interestingly, it's clear from that graph that about 1.5 million in 2021 are excess deaths likely from COVID-19, but that's not relevant here.
Anyway, given that number, that makes the 500k about 5% of total deaths. To me, that seems a reasonable possibility.
Other comments pointed out that the headline here is bogus, and that the 500k isn't direct deaths, but contributory, where the poor air may have made people weaker and thus less likely to survive whatever really ultimately killed them. And even the article only claims that half of that number would have survived with lower pollution levels.
That does decrease the usefulness of the statistic, because it becomes clear that the authors are just trying to make a big number to make their work (and thus themselves) look more important. Not that air pollution isn't important, but this appears to be another example of over-hyping a problem, which does tend to turn people off a lot and maybe that is why you consider this article "nonsense".
So, while the article has the standard hyperbolic attitude, the underlying information is likely correct, when taking into account its own caveats.
It does mean that it's actually not as big a deal as the article would like, though. Useful for someone deciding what level of enforcement to put on polluters (vs. economic interests), but not really something for general people to get upset over.