The Text Style panel in Preview's Markup toolbar should be showing the fonts that are within the System font database, not necessarily every font in Font Book, some of which may not be actually installed, or possibly disabled. You cannot add fonts to Preview itself based on the first sentence, and with the read-only System partition in Catalina and later, you can only add fonts to your local /Users/username/Library/Fonts folder, a location scanned by the operating system in constructing a Font database.
What I see with Preview on macOS 11.6 is every font that appears in my Pages v11.2 font menu, including some Postscript Type 1 fonts.