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The answer is "Yes", it will require VBA. Cells can contain formulas, or hard-coded values, but never both at the same time.
So, if you use an Excel function like TODAY() or NOW(), it is always going to show the current date/time.
If you want to capture the day/time something is last modified, you need to use VBA/.
If you search this forum on "Date Stamp" or "DateTime Stamp", you will find hundreds of posts on this, that will show you how to do this (the question is literally asked every day!).