I opened a case with Microsoft because I could not integrate the iOS OneDrive (business) app with the Adobe Acrobat Reader app. After troubleshooting with Microsoft and evaluating conditional access policies, app protection policies, app configuration policies, they determined Adobe Acrobat Reader was trying to sign into OneDrive using Safari browser and since Safari browser is not an Intune approved app, it gets denied by our conditional access policy. If it would use Edge somehow, this would fix this issue. I started looking into this when I saw Adobe Acrobat Reader supports Intune per this Adobe support article: https://www.adobe.com/devnet-docs/acrobatetk/tools/Mobile/intune.html.

Please reach out to me if you can to work thru the issue and potentially fix an issue.