Can a boss tell his staff to apply for others positions because they may not be a good fit where they are?

Yes, a boss can suggest that staff apply for other positions if they believe the employee may not be a good fit for their current role. This approach can be seen as a way to support the employee's career development and ensure they find a position where they can be more successful. However, it's important for the boss to communicate this feedback sensitively and constructively to maintain a positive working relationship.