Back Button Assignment Possible?

i’ve come back to RetroArch after a long stint of using other emulators. Good to see all the development. I’m using an Nvidia Shield Tablet and I just started with it, but I’m still a bit thrown that RA still won’t recognise back button presses still. I can’t even configure it as a keypress in the options, RA doesn’t detect me pressing it when trying to assign it as Toggle Menu. Is this intentional or is there a way I can get RA to acknowledge back button presses?

I am aware I can configure buttons from my gamepad to do this. I’m just seeing if there is any way to get RetroArch to acknowledge the back button.