Currently there isn't a way to bring up a list of contacts that have no active workflows running.
As a workaround, under Contacts, we could filter out contacts that are not active on a specific workflow (using the "Workflow (Active): Is not" filter) and we can add multiple filters for all the workflows using the "AND" filter but it would be cumbersome to list/add all of the workflows especially if the sub-account has quite a number of workflows.
It would be great to be able to filter out contacts that are not active on any workflow at all. Thanks ahead!