LOWER_CLICK QMK CODE

#define LOWCLK_HOLD_LIMIT 400  //configure hold time for LOWER_CLICK. hold for less than 400ms to left click

enum custom_keycodes {
    MACRO1 = SAFE_RANGE,  //start of other macro keys
    MACRO2,
    MACRO3,
    LOWER_CLICK           //custom macro keycode, name it what you want
};

uint16_t lowclk_hold_timer = 0;  //lower_click timer variable

bool process_record_user(uint16_t keycode, keyrecord_t *record) {
    switch (keycode) {
        //other macros
        case BACKLIT:
            //...
            break;
        case LOWER_CLICK:
            if (record->event.pressed) {           //when LOWER_CLICK is pressed
                lowclk_hold_timer = timer_read();  //  mark the time it was pressed
                layer_on(_LOWER);                  //  go to _LOWER layer
            } else {                               //when LOWER_CLICK is released
                layer_off(_LOWER);                 //  leave _LOWER layer
                if (timer_elapsed(lowclk_hold_timer) < LOWCLK_HOLD_LIMIT)
                    tap_code16(KC_MS_BTN1);        //  left click if macro key was held for less than LOWCLK_HOLD_LIMIT ms
            }
            break;
    }
    return true;
}