Always Valid Excel Time of Last Modification in a Cell

This one is crap : https://www.extendoffice.com/documents/excel/954-excel-created-last-modified-time.html

Look elsewhere..

It's simple :

=NOW()

And then, select that same cell, and Format > Format Cells and click on the one that says m/d/yyyy h:mm and then, when you do that, notice that the Type: field has now gotten populated. Click there and change to m/d/yy h:mm unless you expect to live till 9999 AD :)

And of course, it's not perfect :) You guessed it :) If you undo your change, then the cell doesn't retract :)

Who can be a hero and figure this out?