@MatYC Thanks for posting in our Q&A.
For this issue, I agree with RahulJinda. App protection policy will meet your requirement. You can add the ‘business apps’ to the app protection policy and configure the settings under Data protection to prevent business apps sharing data with personal apps
https://learn.microsoft.com/en-us/mem/intune/apps/app-protection-policy-settings-ios#data-protection
For only allow MDM enrolled devices to access specific apps, it is suggested to add the apps in "cloud apps or actions" and select "Require device to be marked as compliant" in Grant access in the conditional access policy.
https://learn.microsoft.com/en-us/mem/intune/protect/create-conditional-access-intune
For preventing personal account to login in outlook, I find there is a setting "Allow only work or school accounts" in the App configuration policy.
Hope it will help.
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