é Showing as &eacute in TextEdit – Fix Encoding Issue

It is in TextEdit help - search for HTML

If you open an HTML file and don’t see the HTML code, TextEdit is displaying the file in the same way a browser would. You can choose to display the file’s HTML code instead.

To display the code in an HTML file:

Choose File > Open.

Select “Ignore rich text commands.”

Locate the file and click Open.

To always view the code in HTML files, choose TextEdit > Preferences, click “Open and Save,” and then select “Ignore rich text commands in HTML files” below “When Opening a File.”

So it seems you have to choose before opening the file.

The format menu has a toggle to switch things for you.

Pressing shift + command + T will toggle the document to plain text mode.

You can also set the default format in the preference pane for the app.