Hi @George Sugden
To use Office Scripts, an administrator must enable them first, it means you need the one of the plans listed in imahe below.
Besides, here is a free add-in you can have a look: Script Lab, this add-ins can be accessed via personal Microsoft account, and let anyone to learn how to develop Office Add-ins.
It lets you to code and run the Office JavaScript APIs alongside your document in Excel, Outlook, PowerPoint, and Word.
For more, please refer to 'Explore Office JavaScript API using Script Lab'.
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