I found a surprisingly simple way to tell whether the user is on MacOS or Windows by checking to see which fonts are installed by default on their system. While there is the possibly the user has a font from the opposite system, it's so unlikely that I don't really care. Doesn't work for Linux (which includes ChromeOS and Android) because there isn't any system-exclusive font that can be relied on. 29/4/25: Turns out there's something similar using emojis rather than system-specific fonts, so I might try something like that one day
