Macos is really big on the document model, where a window is tied to a document (file, a set of data, a list of objects), so Option-Tab to switch between applications, and Option-Backquote for said documents/windows.
That only cycles through open windows for the current in-focus application.
E.g. If I have 2 Excelsheets open and 2 Word documents open, if Word is the current in-focus app ... CMD+` only cycles between the 2 Words documents (and does not cycle the Excel sheets)
E.g. If I have 2 Excelsheets open and 2 Word documents open, if Word is the current in-focus app ... CMD+` only cycles between the 2 Words documents (and does not cycle the Excel sheets)