Change font format (style, size, etc.) of all cells in all worksheets

Welcome to the forum
Your code looks ok

But I noticed that I had a problem with a couple of fonts when I experimented
I found that if I put the name in a variable or in a cell and referred to that ,then it worked
It makes no sense, but there we are!

So try this:

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What you are doing is not the best approach

With a clean workbook, this line

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changes the default normal style without formatting ALL the cells in ALL worksheets

The above does not work if the cells have already had their font names formatted

Like I said, I encountered a problem that I cannot explain with certain font names.

another method that worked every time was to put the font name in a cell, and using the above code (with the font name Arial in cell A1)

replace:

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with:

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It makes no sense that either of the above give a different result to your original code:

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If you are still having problems, I suggest you try a totally different font - and then it proves that your code is not the problem

eg I had no trouble whatsoever with "Lucida Handwriting"
- it worked in your original code and in both of my 2 "minor" variations