Since PeopleTools 8.55 the default interface for PeopleSoft applications is the Fluid interface. While this is very convenient for self service functionality, not all back office functionality is available in Fluid.
This article describes how to revert to the classic interface.
Step 1: Modify Personalization Options
This is done via Personalization Options. Navigate to PeopleTools > Personalization > Personalization Options. Open the Option Category Level PPTL and for User Option HPPC set the default value to Classic via the Set Option Default Value functionality.
Step 2: Change Branding System Options
The second thing that has to be done is to set the Default Branding Theme to DEFAULT_THEME_TANGERINE_ALT via Branding System Options. This can be found here: PeopleTools > Portal > Branding > Branding System Options