We've built a custom system image, and there are a few different ways that systems can be deployed onto a device. Usually, an embedded device has a particular way of doing this. The image can be deployed to a Raspberry Pi by writing the system image file directly onto a storage disk using dd or similar. Other devices might need to be deployed by writing the filesystem to a formatted disk, or even as low level as using JTAG.
Deploying to an embedded system
OpenEmbedded
If you plan on using Qt with OpenEmbedded, you should be aware of the ​meta-qt5-extra layer, which contains desktop environments such as LXQt and even KDE5. I personally use both environments and switch back and forth between the two on my desktop...
