zmk-config/config/combos.dtsi

/*                KEY POSITIONS

  ╭───────────────────────╮ ╭───────────────────────╮
  │  0   1   2   3   4  5 │ │  6   7   8   9  10  11│
  │ 12  13  14  15  16  17│ │ 18  19  20  21  22  23│
  │ 24  25  26  27  28  29│ │ 30  31  32  33  34  35│
  ╰───────────╮ 36  37  38│ │ 39  40  41╭───────────╯
              ╰───────────╯ ╰───────────╯            */
compatible = "zmk,combos";

num1 {
    key-positions = <13 1>;
    bindings = <&kp N1>;
    layers = <0>;
};

num2 {
    key-positions = <14 2>;
    bindings = <&kp N2>;
    layers = <0>;
};

num3 {
    key-positions = <15 3>;
    bindings = <&kp N3>;
    layers = <0>;
};

num4 {
    key-positions = <16 4>;
    bindings = <&kp N4>;
    layers = <0>;
};

num5 {
    key-positions = <17 5>;
    bindings = <&kp N5>;
    layers = <0>;
};

num6 {
    key-positions = <18 6>;
    bindings = <&kp N6>;
    layers = <0>;
};

num7 {
    key-positions = <19 7>;
    bindings = <&kp N7>;
    layers = <0>;
};

num8 {
    key-positions = <20 8>;
    bindings = <&kp N8>;
    layers = <0>;
};

num9 {
    key-positions = <21 9>;
    bindings = <&kp N9>;
    layers = <0>;
};

num0 {
    key-positions = <22 10>;
    bindings = <&kp N0>;
    layers = <0>;
};

c_esc {
    key-positions = <15 16>;
    bindings = <&kp ESC>;
    layers = <0>;
};