Error activating XKB configuration for German Macintosh layouts

[martin-braun]

Using Macintosh (German) or Macintosh (German, no dead keys) will make an error window popup:

Error activating XKB configuration.
There can be various reasons for that.

Which results in the US layout being used.

xprop -root | grep XKB returns

_XKB_RULES_NAMES_BACKUP(STRING) = "evdev", "macbook78", "de", "mac_nodeadkeys", "lv3:alt_switch,terminate:ctrl_alt_bksp"
_XKB_RULES_NAMES(STRING) = "evdev", "macbook78", "de", "mac_nodeadkeys", "lv3:alt_switch,terminate:ctrl_alt_bksp"

gsettings get org.gnome.libgnomekbd.keyboard model:

''

gsettings get org.gnome.libgnomekbd.keyboard layouts:

['de\tmac_nodeadkeys']

gsettings get org.gnome.libgnomekbd.keyboard options:

@as []

More context: https://forums.linuxmint.com/viewtopic.php?p=2611992#p2611992