Thanks!
I was already messing with xev but with "KBTYPE=freedom" xev was not seeing AltGr beeing pressed. But after reading your post I googled for "Smart Bluetooth Keyboard" pictures to see if my Zaapa BK600 might in fact be "smartbt" instead of "freedom". And it really is!

Xev now sees AltGr (keycode 189) so I just have to use this command: