@Julian, Thanks for posting in Q&A. To configure homepage shortcut, I find the key is com.microsoft.intune.mam.managedbrowser.homepage
For the key you set, it is used to override the new tab window.
Meanwhile, when creating the app configuration policy, please ensure we choose "Managed devices"
In addition, for Edge, please ensure it is deployed via Intune.
Please check the above information and if there's any update, feel free to let us know.
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