From Embedded Wizard point of view there is no need to use an operating system. Any UI application generated by Embedded Wizard can work with or without operating system.
Since the UI application is always running in one main UI thread (see Main Loop), there are no operating system services necessary.
This means, the usage of an operating system and the selection of a dedicated operating system depends on your entire application and your other software parts.
Most of our ready-to-use Build Environments are created to work with non OS (bare metal) or with FreeRTOS, since this is very popular.