The following article refers to functionality in Workflow Builder, which can be found within Natural HR at one of the following locations depending on your configuration:
Administration > HR > Workflows
Administration > HR > Workflows > Workflows
A new option has been added to workflows in Natural HR which allows you to trigger workflows against employees with a manager level job role only. This can be used to restrict a workflow so that it only triggers against such employees.
When building a workflow, the option can be found towards the bottom of the screen, labelled 'Only manager roles?'
Note that this doesn't take account of the employee's user group, only their job role, so it would not trigger against a user with a Manager user group unless they also had a manager-level job role.