Unfortunately the ability to track assignee history after an entry has moved past the step is not currently available within Gravity Flow. It is on our roadmap for development. Until that is an out-of-box feature, neither a view (GravityView) or Inbox/Status block (Gravity Flow) would be able to implement what you are aiming for without some custom code. Likely something along the lines of:
- Use gform_add_meta and gform_get_meta within the gravityflow_step_complete action to track which assignee(s) were assigned on an entry or possibly the one(s) who completed the step.
- Use gravityflow_inbox_search_criteria or gravityflow_search_criteria_status to adjust which entries the block would display based on the new meta that stores the historical assignees.
GravityView likely has an equivalent way to accomplish the last point if using it. Referring to the GFAPI docs for searching for entries will likely help in both cases for examples around the meta query.
Regards,
Jamie