I have Outlook 365 contacts syncing with GrapheneOS and happy to share the solution as it was not straight forward.
- Install Outlook App on GraphenOS
- Go to Search in Outlook App
- Find any existing contact inside Outlook App and tab "Edit"
Next, GrapheneOS will ask to enable permissions, you grant all that will be requested.
If everything is done correctly, in about 5-10 minutes contacts will sync be become accessible inside native Contacts app in GrapheneOS.
You will also find contact sync account appear in the Settings > Password and Accounts > Outlook