The purpose of the 'Starting up a Project' process is primarily to appoint people to the major roles within the project management team. This process ensures that the right people are in place with clear responsibilities before the project kicks off, facilitating effective planning and execution from the outset. References:
PRINCE2 7 Foundation manual and the 'Starting up a Project' process documentation.

In PRINCE2, the management of ongoing changes to the project ecosystem involves adapting the project's approach and scope based on real-time information and challenges that arise during the lifecycle of the project. This step is critical when new tasks or changes in tasks are identified, as outlined by the project manager. This ensures that the project remains aligned with its intended outcomes and can adapt to internal and external influences effectively.
= PRINCE2 7 Foundation Training Manual and official PRINCE2 website documentation