typst predefines these paths for font detection:

1. /usr/share/fonts
2. /usr/local/share/fonts
3. $HOME/.local/share/fonts

The last one is obtained from the dirs crate.

Sometimes fonts are stored in other directories, like on NixOS, for example, where fonts are stored in a totally separate directory. I'm not familiar with font detection, however, I believe the "conventional" way to go about this is by using the fontconfig library, as used by gimp and many other programs. There are a couple of other Rust alternatives I scoped out but they seem all either unmaintained or immature.