We often have Users who only access the system for some approvals. So in general one would say that such users are from type Team Members. In most Projects we therefore create a "Cost-Approval" or "Approval" Role and mostly this Role never has a full License like Finance/SCM/Project,...

Unfortunately this is just true if you don't involve the Free Text Invoice Workflow, because to access this one you would need a Finance License. So my suggestion would be to change this as for most other Workflows (Invoice Journal Approval, Invoice Approval, Purchase Order Approval, Purchase Requisition Approval, Project Invoice Approval,...) and reduce the License Requirement to Team Member.