I mapped Fn+Prog to Key_Sysreq, for the rare occasion I need to do a three finger salute in Linux. It wasn’t working for me, and I was stumped for a while until I compared the output with other keyboards and realised I had the wrong keycode entirely! Linux actually wants the “print screen” scancode, and it’s already present on the default layout (Fn+Z).
But I’m curious to know now, where did this other thing I unearthed come from?
showkey gives me keycode 240 for it and
xev recognises it only as an unnamed keycode 248.