The rich content editor found in many Canvas tools has been updated with a new streamlined design (starting Winter 2021).
The content sidebar of the previous design, which was used to embed documents, images and media, no longer appears at the right of the screen. 
However, these embed functions are still available as buttons above the text area, as well as under the Insert menu. 
If you have a small screen, you may have to click the Options icon (three vertical dots) to see the embed content buttons. 
For more detailed instructions, see the full guides for embedding documents, images and media using the new rich content editor.