We decided to remove this button from the top menu as users indicated they primarily used the Boolean search in relation to specific roles. Having it as an option in addition to the magnifying glass icon was causing confusion. It can be found under the People icon (1) and by selecting Candidate Search (2):
It's still available in the left grey action menu within any project:
It’s important to note that using the Boolean search within a particular role isn’t actually tied to that role. It functions the same as the previous overall Boolean search.
In other words, if you search within one assignment and see a candidate suitable for another assignment, you can still add them to any other assignment from the search results screen, independently of the assignment you are in.