You are installing an Office Add-in that runs on Windows, Macs, and the web versions of Office applications. An older Windows-only version of the add-in is already installed on your computer.
Running multiple add-ins that register the same commands, ribbon controls, or custom functions may cause conflicts, so you must disable either the old or new version. The publisher of the add-in recommends that you disable the older version. The dialog is asking for your choice of which version to disable.
If you select Yes, the new version of the add-in will be installed on all platforms that support Office, including Windows, Mac, and Office on the web. For Outlook add-ins, the add-in will be installed on classic Outlook for Windows, new Outlook Windows, as well as Mac and Outlook on the web. The old Windows-only version will be disabled.
If you select No, the following things will happen:
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The new version of the add-in will be installed only on Mac and Office on the web. For Outlook add-ins, the add-in will be installed on Mac, Office on the web, and new Outlook for Windows.
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The old version of the add-in will continue to work on Windows. The new version will be disabled on Windows (and on classic Outlook on Windows).
You can change your decision later with the following steps:
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In the ribbon of Office application where the add-in is installed, navigate to File > Options > Add‑ins.
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Select a type in the Manage drop down list, and then select Go.
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Use the dialog that opens to enable or disable an add-in. For further information, see Add or remove add-ins in Excel. (Although the title refers to Excel, the guidance applies to all Office applications.)
For further help
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Review your organization's add‑in policy in the Microsoft 365 admin center.
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Contact your IT support or the add‑in publisher with screenshots and log files.
