Thunderbird has RSS integrated, which could be quite neat once that synchronizes.

If you don’t want to spend the time, you could have simply critiqued the image for being hard to read and interpret, as you are doing now - and requested they provide the source of the image (or the data). That would have been perfectly valid - as this image has seemingly gone through a lot of jpeg-ification and screeshotting, making captions and labels hard to read.

While not understanding French is understandable, Google Translate and other tools can help with that nowadays. You ought to be careful when levying critique on a post, and ensure it is valid. Your mistake was noticed by me in this case, but this could very well be the misinformation against which you caution.

Regarding the laziness in sourcing: I agree that sourcing is not properly provided here. A reverse image search surfaces that many of the plots are available here and refers to the source also stated on the image (Apur), which seems to be an entity with regularly does analyses regarding mobility in Paris, which has analysed these topics before. Whether you trust this source is still up to you, but the source is not simply an anonymous person on the internet.

Reading the annotations on each of the plots, these are all average NOx concentrations of the labelled year, not point measurements - as you are insinuating. Furthermore, the color scales match up too. (edit) Do note: the more recent plot is zoomed in though and scales are much less clear!

I think it is fair to say that recent policy changes, like rejecting private vehicles from the center and promoting active transportation work. Though aftereffects of COVID (work-from-home) may be a contributor too.