Good morning, @kelly_thompson ...
As long as you are continuing to type content in the RCE (Rich Content Editor) and have not saved your edits, you can always use the keyboard combination Ctrl + Z (Option + Z on a Mac?) to "undo" your typing. But, once you save your edits on any content within Canvas, you can no longer "undo" those changes with the Ctrl + Z keyboard combo. Also, if you press Alt + F9 while your cursor is in the RCE, a hidden text-based menu will appear (File, Edit, View, etc.). If you click on "Edit", you'll see the "undo" and "redo" options listed there...with their keyboard shortcuts. Again, these only apply if you've not saved your work.
Finally, I'm not sure if you've ever used this feature of Canvas "Pages", but you can return to previous versions of your pages with just a click or two of the mouse. Check out this Guide: How do I view the history of a page in a course? - Canvas Community. This only works for "Pages". It does not apply to "Assignments", "Quizzes", "Discussions", etc.
I hope this will help a bit, Kelly. Sing out if you have any other questions about this...thanks! Take care, stay safe, and be well.