Single nucleotide polymorphism Puns

Hello there

I'm reading this article the "genetic link between gender dysphoria and sex hormone signaling" (https://academic.oup.com/jcem/article/104/2/390/5104458?login=true) and the article, says that the main outcome was measured this way: "Genomic DNA was genotyped for repeat length polymorphisms or single nucleotide polymorphisms."

English isn't my first language so, it's a bit difficult to understand this fully. I also haven't been taught this yet (I don't remember our teacher ever talking about it), so I was wondering if anyone here could explain it to me as I can't find any good explanations online.

Thanks in advance

https://academic.oup.com/jn/article-abstract/151/4/763/6000020

Apologies that I don't have details on the specific study I am referencing but I heard a lecture about investigators exploring the association between copy number variations and cardiovascular disease. However, their data showed they investigated specific SNPs which were used as a proxy for CNV calling. I'm wondering how that works or if anyone can ELI5 why you would look at SNPs and not just CNVs themselves since aren't CNVs based on a larger segment of genes while SNPs are alterations in a single base pair? Please let me know if I am not phrasing this correctly I am new to genetics and not comfortable with the terminology yet.