@Alex Findlay, Thanks for posting in Q&A. Based on my testing, I find the package identifier of the app we added in Intune portal is included in the app URL when we search the app in Microsoft store website.
https://apps.microsoft.com/detail/9nzvdkpmr9rd?hl=en-us&gl=US
I think you can search the app in the following link to get the package identifier.
https://apps.microsoft.com/home?hl=en-us&gl=US
Hope the above information can help.
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