You can quickly exit manual formatting by pressing CommandCtrl+Shift+X. For example, if you have pressed CommandCtrl+B to apply the bold typeface to the text that you type, press CommandCtrl+Shift+X to return to the default character format of the paragraph.
要重置现有文本的所有直接格式，请选择文本，然后再选择菜单命令「格式 - 清除默认格式」。