keyboard: Drop "Left Alt" as compose key option
One of the compose key options in Settings -> Keyboard (actually the first one in the list) is "Left Alt". However, that option does not exist in XKB:
$ cat /usr/share/X11/xkb/rules/evdev.lst | grep compose: compose:ralt Right Alt compose:lwin Left Win compose:lwin-altgr 3rd level of Left Win compose:rwin Right Win compose:rwin-altgr 3rd level of Right Win compose:menu Menu compose:menu-altgr 3rd level of Menu compose:lctrl Left Ctrl compose:lctrl-altgr 3rd level of Left Ctrl compose:rctrl Right Ctrl compose:rctrl-altgr 3rd level of Right Ctrl compose:caps Caps Lock compose:caps-altgr 3rd level of Caps Lock compose:102 The "< >" key compose:102-altgr 3rd level of the "< >" key compose:paus Pause compose:ins Insert compose:prsc PrtSc compose:sclk Scroll Lock
Consequently, if you select "Left Alt" as your compose key, it won't work, so that option should be dropped.