Ideally , screen flow are used to serve the purpose of being operated by same operator .It is configured only in the start shape. It can be routed only to operators and the same (only one) operator is responsible for completing all the steps.I do not think pyTransferAssignment can be used directly to transfer to another operator if using screen flow.
You can check below thread which might be helpful for your case :
I have a screen flow with 3 screens(assignments). I must be able transfer the case(using pyTransferAssignment) to any operator. All the 3 assignments in screen flow should be assigned to the new operator.
The issue im facing is only the current assignement(screen, say 1st screen) gets assigned to new operator when transfer assignment flow action is called. The other screens will still be in worklist of old operator.