Wikipedia says that New Scientist publishes articles which are not peer-reviewed.
But I found no information about "Scientific American" (SciAm) and "Popular Science" (PopSci).
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From the Scientific American website:
Generally speaking, SCIENTIFIC AMERICAN presents ideas that have already been published in the peer-reviewed technical literature. We do not publish new theories or results of original research.
Please allow six to eight weeks for the review process.
From this and other submission instructions on that page I conclude that the manuscripts undergo a general review that is probably aimed at accuracy and style, which is different than typical scientific peer-review of original research.
No scientific peer-review is mentioned in the relevant page on the Popular Science website either.
Neither journal is a peer-reviewed scientific journal, both are popular science journals. So (1) they don't publish original research and (2) the aim of the review process is completely different. In particular, reviewing is done to ensure that the article is suitable for the scientifically minded public, i.e. avoids complicated math and difficult terminology, but hardly to scrutinize correctness (or even originality).
These are not academic journals, but magazines which report on stories of interest to the public. They source their stories from peer-reviewed academic papers from various journals.
That is, they are not the primary place of publication or the original paper for any of the research presented within; they are simply reporting on research published first elsewhere.
So. Is the research they cover peer-reviewed? By and large, yes. But it has been peer-reviewed elsewhere, in another form - and has been reported on by a journalist specialising in science, who did not write the original publication or do the experimentation themself but is seeking to expose it to a larger audience.
You are given the opportunity to consult the original publication; each story that originates from a scientific publication should cite its source.