Assume you’ve installed the package xf86-video-qxl.
Inspecting the package contents, I see only drivers and a library file, no configuration files.
So, it looks like qxl is implemented only as something to be called from a command line(which is in effect calling in User mode), and in general qxl is used only when you run SPICE (pls verify this is what you are trying to do).
This suggests that the way to implement is to call the qxl driver along with any desired options from within your connection command.
You’ll need to post the exact command you’re running for others to evaluate.