As in the screenshot below, there is a problem on macOS where typing Korean in a Chromium-based browser produces a strange special character (a ligature? a box? a hwatu card?). It doesn't show up while you're writing in Chrome, but it is visible in Safari and on Windows. This causes trouble when you're writing a document meant for the public.
Here are the workarounds.
- The special character is displayed as-is in Safari. So proofread once more in Safari and delete the character.
- Use the
Gureum input method.
Source: 
https://discussionskorea.apple.com/thread/254883494?sortBy=best