excel unable to change font and color

Hi @Eric Sin Han Wei
Thank you for posting your question in the Microsoft Q&A forum.
To better assistance, could you please confirm detailed information below:

• Does this issue happen in all Excel files or only in a specific workbook?
• When you try to change the font or cell color, does it work in a new blank workbook? If it doesn't happen the issue is likely in the original file, if it happens in a new blank workbook, we’ll adjust Excel/Windows settings.
• Are you seeing the message “Too many different cell formats” every time, or only sometimes?

In the meantime, I would like to suggest some steps you could try:

1/ Install the Latest Excel Update

Older builds of Excel had bugs that caused duplication of built-in styles when copying sheets between workbooks. Updates often include fixes for these issues.

• Open Excel => File => Account.
• Click Update Options => Update Now.
• Restart Excel after the update completes.

2/ Remove Conditional Formatting

Excessive or redundant conditional formatting rules increase unique format combinations.

• Go to Home => Conditional Formatting => Manage Rules.

Select This Worksheet and delete unnecessary rules.

Reapply only essential rules with precise ranges (avoid entire columns/rows).

3/ Clear All Cell Formatting

Resetting cells to default style helps reducing format complexity.

• Press Ctrl + A (select all) => Home => Clear => Clear Formats.

Reapply minimal formatting afterward.

4/ Apply Standard Font Style

Using multiple fonts and fills creates unique format combinations.

• Apply a single font (e.g., Calibri 11) across the workbook.
• Remove unnecessary fill colors and borders.

5/Open the problem workbook in Excel Safe Mode

• Press Windows+R, type excel /safe, press Enter. Open the file and try changing colors.
• Tell me if Safe Mode helps.

6/ Repair Excel Application

Navigating to Control Panel => Programs and Features then looking for Microsoft 365 Apps (It can be a little difference between versions, could be Microsoft 365 Apps, Microsoft Office, and so on), right-click and choose Change

Then choose Online repair 7/ Save as Binary Workbook (.xlsb)

Reduces file size and simplifies internal structure, lowering risk of style corruption.

Navigating File => Save As => choose Excel Binary Workbook (*.xlsb).

Important note: Always back up the workbook before applying cleanup steps.

Please understand that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.

Your detailed response will help us diagnose and investigate the issue more efficiently. If I misunderstood what you’re looking for, feel free to let me know or share a screenshot. I’d be happy to help further! 

Thank you for your cooperation. I'm looking forward for your reply.

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