Section 29.14 Icons
<icon> element is built around the Font Awesome font collection. The LaTeX
fontawesome package contains all the necessary font files (for use with both
xelatex), and a style file that interfaces, in a semi-elaborate way, with the font files. If you have installed this LaTeX package, and the fonts still seem unavailable, figure out how to adjust your LaTeX setup or your system configuration. Simply installing a font file, such as the more recent Font Awesome 5 is not going to work. See Chapter 38 for more about fonts in LaTeX.