Option-Left/Right Arrow doesn't work
The problem has been solved by switching the input source from "Unicode Hex Input" (my major input source) to "U.S.". I think some option based shortcuts can't function as usual with "Unicode Hex Input". You can update the input sources by searching "unicode" to be directed to system preferences -> Keyboard. Click "Input Sources" and remove other input methods that might be causing the error. Then open a new window for the program you want to test.