Brief on direct transfer:
Different approaches of master data migration has been provided by SAP in S4 HANA. In S4HANA 1909 version, new approach has been provided by SAP i.e. directly transfer data from SAP source systems to S4 HANA via RFC connection. Here explaining the process on scenario 1 which is "SAP ERP to SAP S/4HANA"
Required Roles
In SAP source system required composite role is SAP_DMIS_OBT_REMOTE.
In SAP S/4HANA target system, user with the role SAP_DMIS_OBT_MASTER is required. And also the role SAP_BR_CONFIG_EXPERT_DATA_MIG for the front-end server.
For using the migration object modeler (transaction LTMOM), role SAP_CA_DMC_MC_DEVELOPER is required in the SAP S/4HANA system.
FIOR app activation:
Even though after installing required components, until FIORI app get activated, we can’t see the Data Migration app in FIORI.
T.code to activate the FIORI app: /IWFND/MAINT_SERVICE (basis activity)
Data Direct Transfer Process step by step:
To start data migration, project should be created in FIORI.
Create new migration project
Now select the migration object for which you want to migrate the master data, here selected Cost center for migration
Click save, then it will ask whether any predecessor objects also to be migrated. If want then click “Add” else click “Do Not Add”
You can see predecessor details by clicking on “View details”

Then Click Add
Cost center object added
Here you can see who created, date, source system
Click on Cost Center project, then it will display list of migration objects in cost center. As no activity has been started for migration you can see object as “Not Ready for Processing”
Click on show activity tracking
You can see migration project preparation status as “Started”. Once it completed then activity will move from active to completed
After prepare migration activity completed, here can observe “Not ready for processing” will disappear. It means migration object is ready for processing.
Once the activity tracking status as Finished, then you can see the Select Data option under Actions
Click Actions and Select
Then it will display pop window showing the company code for which master data is migrating.
Select Start Selection, then you can see Select data activity started in activity tracking
When an activity started an background job will get generated and process
NOTE: when ever each activity started, then background job will get generated
Once the activity completed, then active will be 0 and completed it will update as below
Here if observe the activity status as “Failed” because while processing any migration object, if connectivity not available or failed between source and target systems, then migration will not happen and status will be failed.
Click on settings to see the migration project related details as below

Go back and Click on FICO Cost center migration object
It will show you details of object description, table structure, object activity history

Now go back to migration object. Here you can see successful instances for selected data.
Click on instances to see the list of objects processed. As the selection task completed, mapping tasks updated with Open as 10

Click on arrow next to success to see full information on the object. Here can see the cost center master data and text details
Go back to migration object screen
Click on Action->Mapping Tasks. It will display the tasks which can be verified and mapped
Select all tasks
Click on mapping tasks, now can see each field value mapping between source and target system
If want to maintain same source cost center number in target system also or if want to use new cost center in target system, based on that update the target cost center

Now select all and click Confirm, here we confirmed only single value mapping
Above just to show you how mapping will display and to confirm.
Go back, Select all and confirm all filed values
All value fields confirmed
Go back, now see mapping tasks Open items are 0 and Done are 10
Select cost center migration object
Select action-> simulate-> All instances
Simulation processing started
Activity tracking shows Simulation data finished
Here Simulation Errors are 0 and Successful are 2 (here out of 10 records I excluded 8 and selected only 2 for simulation)
Click on Successful, so that you can see successfully simulated master data
Now migrate your data. Once migrated then cost centers will get created in target system
Here you can see Migration not started are 2
Select Actions->Migrate->All instances
And now Migrate data finished
Final step is, go to CFIN (target system), check cost center master data which was migrated.
Table CSKS updated with new cost centers.

This document helps you to understand end to end process of direct data transfer.