It is possible to define "Intercompany" in a workflow. But the Intercompany General Journal does not have any action buttons to send approval request (also not reject and deletage).
Please add those action buttons also to the Intercompany General Journal, so that this can be used with the standard functionality.

Similar idea for Recurring General Journal:
https://experience.dynamics.com/ideas/idea/?ideaid=0aeee996-c999-e911-80e7-0003ff68d318

Similar idea for FA G/L Journal
https://experience.dynamics.com/ideas/idea/?ideaid=5acb93ea-e459-e811-bd6d-0003ff68b9c6