The advantage of having Undo and Redo on the Quick Access Toolbar is that there they're always available, even if Word has switched you to another ribbon such as Table Layout or Shape Format. If you really must have them on the Home ribbon, though, there is a way.
In Excel on Windows (Microsoft 365): Look at the very top-left corner of the Excel window, above the ribbon. The Undo button is on the Quick Access Toolbar and looks like a curved arrow pointing left. You can also use the keyboard shortcut Ctrl + Z to undo your last action. Press it repeatedly to undo multiple steps.
If the red text/formatting was applied manually (for example, red font color or underline style), use undo as above, or select the text and change the font color/underline back to the desired style.
How do I undo an action quickly in New Outlook? - Microsoft Q&A
Note that there are no dropdowns that you can drop down to see the list of commands you will be undoing and the order in which they are undone, such that you can choose how far back in the list to undo.
In Excel the dropdowns for Undo and Redo disappeared in the Quick ...
The undo button is missing. The program doesn't make sense. I found the undo button draw and in the customized settings the command is listed, but it does not work, it only shows as light black and not dark black under draw function. Can I turn back on the undo button back where it was before the update?