A window hidden behind other windows is still open, so start with an overview rather than reopening the document. Open Mission Control to spread visible windows into a selectable view, then choose the target by content, title, and application.
Narrow the overview when you know the app
If the desktop contains many windows, activate the application and use App Exposé to see that app’s windows. The Window menu can also expose titles that are unreadable in small thumbnails. Command-backtick is faster when the set is small and distinct.
When thumbnails look alike, do not rely on position: overview layouts can change. Look for the document name, browser-window name, repository path, or a unique piece of visible content.
Check states that are not simply covered
A minimized window may be represented in the Dock or the application-specific window view. A full-screen window occupies its own area in the Spaces bar. A hidden application and a closed document are different states. If selecting the application shows only the menu bar, inspect these states before creating another window.
Prevent the same search next time
Give similar windows better titles where the source app allows it. Keep only current project windows in a project group and close obsolete duplicates after saving them. Use a title-searching switcher if text is a stronger clue than appearance.
Wallo can display current window previews when macOS permissions and capture conditions allow, but a preview is an aid rather than proof of identity. Confirm the selected window before acting, especially when several previews are nearly identical.