Fly automatically uses the Graph API for migrations in the following scenarios:
Exchange Online Migration: If either or both the source and destination mailboxes are licensed as Exchange Online Kiosk, Microsoft 365 and Office 365 F1, or Microsoft 365 and Office 365 F3, Fly automatically uses the Graph API.
Gmail Migration / Exchange On-Premises Migration: If the destination mailbox is licensed as Exchange Online Kiosk, Microsoft 365 and Office 365 F1, or Microsoft 365 and Office 365 F3, Fly automatically uses the Graph API.