mine is an optimized german keyboard layout.
mkdir -p ~/.config/xkb/symbols curl https://dl.neo-layout.org/custom_mine_2.39 > ~/.config/xkb/symbols/custom
Add keyboard layout:
GNOME Settings > Keyboard > Input Sources > Add Input Source > Other > A user-defined custom Layout > Add
Choose keyboard layout with the drop-down menu in the top right of the GNOME Shell status bar.
If the keyboard layout cannot be found, press the litte eye icon or „View Keyboard Layout“ next to the „A user-defined custom Layout“ entry in GNOME Settings and find the error message in the systemd journal.
bash$ journalctl -et org.gnome.Settings Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-338] Couldn't find file "symbols/custom" in include paths Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-338] 1 include paths searched: Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-338] /nix/store/3kj098kkfh4mw4d70yjqg1flxzj3xw21-xkeyboard-config-2.46/etc/X11/xkb Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-338] 4 include paths could not be added: Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-338] /home/clerie/.config/xkb Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-338] /home/clerie/.config/xkb Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-338] /home/clerie/.xkb Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-338] /etc/xkb Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-661] Couldn't process include statement for 'custom' Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-769] Abandoning symbols file "(unnamed map)" Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: Failed to compile xkb_symbols Apr 08 20:08:07 helium org.gnome.Settings[25083]: xkbcommon: ERROR: [XKB-822] Failed to compile keymap