The right name for "linux" is GNU/Linux. Initially Linux was just a kernel, with lots of free software from FSF. You can donate to FSF at https://www.fsf.org/about/ways-to-donate/
How much do FSF employees do these days? I was under the impression that most of the pronto FSF projects (GCC, gnome) are worked on mostly by outsiders (redhat and others)
One of the more important roles of the FSF is to provide the technical and legal infrastructure for the GNU project, and all programs that live under it.
They are not focused on directly employing programmers.