Can you program QtPlasmaC to make a bevel cut and how to do it.
No, not easily, but you can use CAM software to do that and use it with QtPlasmaC.
There was talk of adding 4th axis for cutting square tube, i do not recall it was actually done.
In general, that is not something LinuxCNC should do, it is CAM's responsibility to output correct gcode for the machine, LinuxCNC is for running that gcode on the actual machine.
Even with CAM it is quite complicated to do 4th and 5th axis as that changes actively tool center point on all directions, so it will not be just click to export gcode.
Sorry i can not help more.
