I read that you can do this by choosing Customize during installation but I didn’t see any option to actually choose a software. The software that I want to install is Math and I am on Windows 10.
You don’t understand an important thing: LibreOffice is one single program. Calc, or Writer, or Math, or else are basically just frontends sharing the same core libraries. So, you can only install it all.
and yet quit any LO app in MacOS and the editor in question quits (Writer for example) but LO continues to appear in the dock and needs to be quit separately.