Projects can be deleted from the project settings inside a project.

You can go to project settings (a gear like icon on the top right corner of the project plan page)--> General information→ Workflow management

You will find the ‘Delete project’ option here.

How to bulk delete projects?

This can be done by setting up a global automation. 

You can set the condition as per your requirement of when you want the projects to be deleted.

For eg- If you want the project to be deleted if the project start date is more than 60 days ago then you can set it up in this way- ‘When project created’ should be the trigger,  ‘project start date is more than 60 days ago’ is the condition and ‘delete project’ is the action.