Qt Designer
Qt Designer is normally used by developers to design GUIs for desktop applications, while Qt Quick Designer is usually used for mobile and embedded platforms. With that being said, both formats run just fine on both desktop and mobile formats, the only difference is the look and feel, and the types of languages used.
The GUI file saved by Qt Designer carries the .ui extension, which is saved in XML format. The file stores the attributes of each and every widget placed by the GUI designer, such as position, size, margin, tooltip, layout direction, and so on. It also saves the signal-and-slot event names within itself for easily connecting with the code in the later stages. This format does not support coding and only works for Qt C++ projects, namely widget-based application projects.