Currently, in order to temporarily enable the Undo button, you must switch the Plan Mode from Autosave to Manual Save. That then only tracks changes for the current working session and you also introduce the risk of not saving desired changes.
Microsoft and Google Products provide autosave in combination with a version history that tracks all changes and stores them as a version history, so that you can always undo changes, even days after you've made them.
Workfront already has autosave and an Update history audit trail, so it would be helpful if that Update history could be put to use to enable an Undo button even when Auto-save is on.