When you withdraw your application on Get on Board, your profile will be moved to the "discarded" phase of the recruitment process. Although no direct notification is sent to the company, the company will be able to see the reason for the rejection (that you withdrew your application for the position) and will not be able to send you direct messages from the platform.
When you apply for a job on Get on Board, your profile enters the company's talent pool. If you withdraw your application, and your profile is attractive to the company, they may contact you via email or other means.