By changing modality, UI element can be presented in a different way to the user. For example, certain screen elements and its supporting information can be delivered as overlay or popup such as a GDPR compliance & cooky disclaimer often shown on websites.
Structure of the page or screen can also be effectively used to direct attention on the desired UI element. This approach is ususally used in newspaper websites to showcase top stories.
Transparency is used mostly in buttons and overlays. This is effectively made use of in lock screen overlay app notifications which attract the attention but still they are see through so you lock screen wallpaper etc are still visible.