If you’re looking for a plain text editor in macOS, you can use the TextEdit app that comes with the operating system. TextEdit’s default file format is rich text. But you can change it to use plain text.
Go to TextEdit > Preferences and change the Format settings to “Plain text”. That’s it.
Some people likes to keep their notes in plain text format rather than rich text, as plain text file can be easily open in all computer systems and there is no worry of format obsolescence.
You can also use a plain text editor to remove text formatting from documents and web pages. Copy the rich text from Notes, Pages or web page into the clipboard. Then paste it into plain text editor to remove all formatting.