Keep it simple, stupid

kss.c

//for understanding weekday2 there are more details to think about
const char *weekday2(int dayOfWeek)
{
    if ((dayOfWeek < 1) || (dayOfWeek > 7)) {
        ESP_LOGE(TAG, "dayOfWeek must be in range 1..7");
        return NULL;
    }
 
    const char *weekdays = {
        "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"
    };
    return weekdays[dayOfWeek - 1];
}

// Simple, easy to understand
const char *weekday1(int dayOfWeek)
{
    switch (dayOfWeek) {
        case 1: return "Monday";
        case 2: return "Tuesday";
        case 3: return "Wednesday";
        case 4: return "Thursday";
        case 5: return "Friday";
        case 6: return "Saturday";
        case 7: return "Sunday";
        default: ESP_LOGE(TAG, "dayOfWeek must be in range 1..7");
    }
    return NULL;
}