While apparently Fontemon is pre-computed (https://github.com/mmulet/code-relay/blob/main/markdown/HowI...), font files are Turing complete (https://gwern.net/turing-complete#fn4). The grandfather of computer fonts, PostScript (as implied in the name) is a computer programming language in itself (but optimized for drawing stuff to be printed in paper), and TTF, OTF (both font formats) and PDF (document format) are also Turing-complete.
Fun (or scary, depending on how you look at it) fact: the TrueType hinting language (which is not based on PostScript) is in of itself another Turing-complete language, so in TTF files there are two separate Turing-complete languages (the PostScript-based one and the hinting language). This is the reason why Microsoft in the '90s begs you to not install fonts willy-nilly.
Fun (or scary, depending on how you look at it) fact: the TrueType hinting language (which is not based on PostScript) is in of itself another Turing-complete language, so in TTF files there are two separate Turing-complete languages (the PostScript-based one and the hinting language). This is the reason why Microsoft in the '90s begs you to not install fonts willy-nilly.