We have come across both an "Idea Approval" and "Project Approval" button in certain MUX Blueprints. We cannot find any instructions on how these were added to the Blueprints or templates in order to recreate in our own environment.
Release : 16.1.1
If you have a process associated with the object it will be available to add in Action Items in MUX Blueprint. Someone must have created one in Clarity environment... you check via in Blueprint > Action Items there should be processes for Project and Idea. When setting up and it's quick just don't forget to Publish.
Supporting Documentation:
Create a Process in MUX through Blueprint
https://knowledge.broadcom.com/external/article?articleId=258496