If you can’t enter certain characters
Make sure a Japanese input mode is selected in the Input menu in the menu bar.
While using the Japanese input source, click the Input menu in the menu bar, then choose Open Japanese Preferences. Make sure the typing mode you want to use (Romaji or Kana) is selected in the “Typing method” pop-up menu.
In the Keyboard Viewer, make sure the characters displayed correspond to the characters you press on the keyboard.
If you have another keyboard, try using it. If characters displayed correspond to the characters you press on the second keyboard, the original keyboard may not be working correctly.
If you think that converting every character may be causing certain characters not to display, turn off Live Conversion. Instead, use traditional conversion.