Introducing Non-Greedy search in your selectors instructs it to search through all the active windows or browser instances that match the top-level tags of your selector, and not just the window instances in focus. Non-Greedy search makes use of the idx() attribute, which needs to be included in the top-level tag, as follows:
<idx='*'> searches through all active window instances for the element matching the top-level tag attributes.
Please note that the <idx='1'> option only searches through window instances in focus.
UiPath Documentation
Exam Topic: Describe how Tags and Attributes, Dynamic Selectors, Anchor Base, etc. are used in UI Explorer to create a robust selector in the Default, Active Accessibility, or UI Automation frameworks