Someone I coauthored a paper with a couple of years ago has recently posted a new preprint (with some new authors) in which several paragraphs have been copied from this earlier paper; at least two paragraphs have been copied verbatim, with several others copied with only trivial modifications made to certain words. The new paper does cite the old paper, but only in the introduction (i.e. not within any of the relevant sections in which text has been copied), and in particular does not give any indication that any of the text has been copied from elsewhere (e.g. there are no quotation marks, no "as first described in...", etc.).
Here's where it gets slightly more subtle: I actually have proof (in the form of records from our collaborative Overleaf document) that all of this text was written by me, and not by my coauthor. However, despite writing this text, I am not credited anywhere within this new paper, except for the aforementioned citation to our collaborative paper in the introduction (my name does not even appear in the acknowledgements).
A couple of questions, then:
(1) Does this constitute plagiarism?
(2) Irrespective of whether this formally constitutes plagiarism or not, what can/should I do about it (if anything)?