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...
