Projects cannot be deleted in PPO. Projects are treated as special cases in PPO since they play a prominent role in relation to other entities. Projects can be linked to other projects (e.g. parent projects) while project-related entities link to projects (for example issues, risks, tasks, time entries, approvals etc).
If projects were allowed to be deleted, this would create an issue when viewing the history of an item which is essentially the audit trail.
If you do however have the need to remove a project that was perhaps logged in error or is no longer required, you can mark the project as inactive. Select the Project, click on Edit.
Then un-tick the Active tickbox.
Once you have marked a project as inactive, the item will not be deleted but will instead be hidden behind the Global filter. On the screenshot below there are 18 Active projects.
Once you have un-ticked the Active tickbox you won't see the inactive project. In the screenshot below it now shows 17 Active projects.
You will still have access to the project if needed. Simply remove the global filter for Only Active Projects.
For more information on global filters, please see the following knowledge base article.