There is an upcoming feature (Cross-Tenant SharePoint migration: https://learn.microsoft.com/en-us/microsoft-365/enterprise/cross-tenant-sharepoint-migration?view=o365-worldwide) that should support this operation. Also there is documentation that explains the possible strategies that you may follow:
https://learn.microsoft.com/en-us/microsoft-365/enterprise/microsoft-365-tenant-to-tenant-migrations?view=o365-worldwide
Have you checked it?