You can manage who has access to a workflow by making it visible only to certain individuals or permission levels.
Give Access
You can only share workflows with users who have permissions of at least Viewer.
You can decide who has access to the workflow by their permission level, or you can choose a specific person.
From the workflow, click Share with to choose who can access the workflow.
Remove Access
From the Workflow, click the x to remove a permission level or person's access to the workflow.
When someone doesn't have access to a workflow, they won't see it in the list of workflows or see any of the workflow's cards from a profile page. Unless you've told them about it, they won't even know the workflow exists.