Fallback fonts don't work for Korean. Take this example "중요성".
When you type them in AE on a Text Layer with a non-Korean font, you get a blank layer,

The Text Layer should automatically fallback to a font that supports CJK characters. This works for other languages. Unfortunately these Korean gylphs are unsupported in Myriad Pro and Times New Roman, so it must be patched with a supporting font.
Here is an Korean font from Adobe Fonts which you could use: https://fonts.adobe.com/fonts/mgothic-210
Continuation of previous bug report: https://community.adobe.com/t5/after-effects-bugs/after-effects-fallback-fonts-broken-for-many-langu...