I have a Mac and use Safari as my default browser. Across my Mac, despite having several fonts that support it, 옛한글 does not render how it is supposed to. For example ᄀᆞᇫ다 just appears as a string of text with 다 next to it. How can I fix this for Safari and or my entire computer so that 옛한글 renders correctly?
For some reason, the text engine on macOS doesn't fall back to additional CJK fonts that have better range of supported glyphs. You could probably fix Safari by a custom CSS injection, but I'd suggest you go with Firefox, which provides a relatively easy way to set custom fonts for specific languages.
See https://support.mozilla.org/en-US/kb/change-fonts-and-colors-websites-use . I tried Noto CJK and it worked.