I just rebuilt gqrx, but no different - it still needs type = other etc.
I tried running gqrx displaying on the XU3’s display (not remotely), and it is totally useless. I hit the well known “black screen bug” - hardkernel have failed to fix this in well over a year, so I am abandoning the XU3 - and I strongly recommend no-one purchases the XU4 either, unless you have no need for local graphics.
Now time to find a spare, fairly powerful Intel PC - great pity, but the Mali GPU simply does not work reliably, and I want a dedicated machine to go with the LimeSDR.