Agree, I think the CVE site messed up the 2021 year and included summary of all years. For previous years, they have number of vulnerabilities for a single year. Some years Android and Windows lead, but most years Linux lead, e.g.

https://www.cvedetails.com/top-50-products.php?year=2018

As for what software is covered - CVE list has just pure 'Linux Kernel', which is not far from the whole Windows 10 (kernel and all the apps and services included), by 1489 vs 2489 vulnerabilities from 2015 to 2021.

The myth of less vulnerabilities in Linux is just that - a myth. They are about the same. One can of course slice and dice it to show benefits of one vs another, but if one is honest with themselves, they have to admit one is not much better than the other. Print spooler is horrible, but CUPS had similar vulnerabilities a few years ago.