Operating systems default serif fonts

At least when it comes to web and digital mediums, serifs get less attention than sans-serif fonts, and the vast majority of modern designs use sans-serifs. But there are many situations when sans is not the best way to go, for example long-form content in places like online newspaper editions (for body text) or websites with a classical theme.
You’ve probably seen a css font-family declaration that didn’t include a specific webfont, but just the serif
fallback, and wondered what font will be used on different platforms.
Whether you use a custom font or not, the recommended css font-family declaration calling for serif fonts is:
font-family: "Times New Roman", Times, serif;
In css serif
will return the operating system’s default serif font. Most operating systems have had the same default since early versions, due to the fact that for many years the web was completely serif playground. Custom font declaration (in html, before css and font-family were a thing) did not exist from the begining.
Default serif font in MacOS
Though Times is the default serif that will be used, it seems that at least on Mojave and Catalina, Times New Roman is also pre-installed.
Actually Times and Times New Roman are branches from the same typeface, with minor differences in character design, but Times is hinted and characters will have a much better letter spacing.
Default serif font in Windows
Default serif font in Linux
Many Linux users re-configure defaults to other fonts, so it’s almost impossible to accurately mention defaults. One of the most popular defaults is Noto Serif, due to its amazing language support.