Hi @Gareth Buchanan ,
What version of Office did you use?
As far as I know, PowerPoint need to enable ink feature, please refer to these support articles:
https://support.microsoft.com/en-us/topic/draw-and-write-with-ink-in-office-6d76c674-7f4b-414d-b67f-b3ffef6ccf53
https://kb.uwplatt.edu/page.php?id=63146
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If you're using correct version of Office, try to install the latest update for Office and check the result.
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