@Charlie Sturman Thanks for posting in our Q&A.
For this requirement, the app protection policy can prevent transferring files from work account to personal account. We can read the following article as a reference.
https://learn.microsoft.com/en-us/mem/intune/apps/app-protection-policy#app-protection-features
In addition, the following article describes how to create an app protection policy.
https://learn.microsoft.com/en-us/mem/intune/apps/app-protection-policies
Hope the above information will help.
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