Hi,
for the monochrome I2C display on the Blackboard check the examples here:
We simply used the luma Python library, not super fast but very easy to use. A much more complex and supercool project is this one made by another forum user:
https://forum2.elk.audio/t/source-a-freesound-community-sampler-powered-by-elk/639
If you want to use more complex displays (DSI, HDMI, etc.), then QT or similar are probably the best choice. I’d recommend following some tutorial on other places for a simple GUI-only embedded application, and then use gRPC / elkpy / elkcpp to hook up the GUI to SUSHI.
Cheers,
Stefano