XKB ctrl + alt como switch level3 xev mostra a saída esperada (parece funcionar) sem sucesso (não funciona)

Question

Eu tenho um layout de teclado alemão e funciona como esperado. O interruptor de Level3 é altgr. Isso é muito inconveniente e eu gostaria de mapear lctrl + lalt como switch level3. Eu fiz um novo tipo, conforme descrito nesta resposta para uma outra questão (relacionada): como ligar o AltGr a < Ctrl > + < Alt >

Mas mesmo que eu tenha realmente tentado muito, não funciona! O que me incomoda é que a saída do xev parece boa, mas eu não sei porque:

KeyPress event, serial 28, synthetic NO, window 0x1000001,
root 0xe6, subw 0x0, time 546490, (19,851), root:(1300,852),
state 0x0, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
XLookupString gives 0 bytes: 
XmbLookupString gives 0 bytes: 
XFilterEvent returns: False

KeyPress event, serial 28, synthetic NO, window 0x1000001,
root 0xe6, subw 0x0, time 546491, (19,851), root:(1300,852),
state 0x4, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
XLookupString gives 0 bytes: 
XmbLookupString gives 0 bytes: 
XFilterEvent returns: False

KeyPress event, serial 28, synthetic NO, window 0x1000001,
root 0xe6, subw 0x0, time 547023, (19,851), root:(1300,852),
state 0xc, keycode 16 (keysym 0x7b, braceleft), same_screen YES,
XLookupString gives 1 bytes: (7b) "{"
XmbLookupString gives 1 bytes: (7b) "{"
XFilterEvent returns: False

KeyRelease event, serial 28, synthetic NO, window 0x1000001,
root 0xe6, subw 0x0, time 547157, (19,851), root:(1300,852),
state 0xc, keycode 16 (keysym 0x7b, braceleft), same_screen YES,
XLookupString gives 1 bytes: (7b) "{"
XFilterEvent returns: False

KeyPress event, serial 28, synthetic NO, window 0x1000001,
root 0xe6, subw 0x0, time 547567, (19,851), root:(1300,852),
state 0xc, keycode 17 (keysym 0x5b, bracketleft), same_screen YES,
XLookupString gives 1 bytes: (5b) "["
XmbLookupString gives 1 bytes: (5b) "["
XFilterEvent returns: False

KeyRelease event, serial 28, synthetic NO, window 0x1000001,
root 0xe6, subw 0x0, time 547651, (19,851), root:(1300,852),
state 0xc, keycode 17 (keysym 0x5b, bracketleft), same_screen YES,
XLookupString gives 1 bytes: (5b) "["
XFilterEvent returns: False

KeyRelease event, serial 28, synthetic NO, window 0x1000001,
root 0xe6, subw 0x0, time 548076, (19,851), root:(1300,852),
state 0xc, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
XLookupString gives 0 bytes: 
XFilterEvent returns: False

KeyRelease event, serial 28, synthetic NO, window 0x1000001,
root 0xe6, subw 0x0, time 548080, (19,851), root:(1300,852),
state 0x8, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
XLookupString gives 0 bytes: 
XFilterEvent returns: False

Eu tentei dois teclados em diferentes sistemas e estou sem ideias ...