error while comparing string in structs with entered strings

fgets() reads also the newline ('\n') character at the end of the buffer (when possible). a newline is added when you press Enter at the console and it will make the comparison fails. from man fgets:

Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer. A terminating null byte ('\0') is stored after the last character in the buffer.

so the content of empName array for input "Steve xyz" will likely to be:

['S', 't', 'e', 'v', 'e', ' ', 'x', 'y', 'z', '\n', '\0', ...garbage]

here a rewrite of the code, basically you have to remove '\n' if it's there. there was also a problem in the initialization of the struct array:

#include <stdio.h>
#include <string.h>

struct employee {
        int cardNo;
        char name[20];
        long salary;
        int age;
} emp[20] = {
        {0, "John Doe", 6500, 25},
        {1, "Steve xyz", 7000, 30},
        // initialize here other 18 structs if needed
};

int main(void)
{
        char empName[30];
        printf("Enter your name\n");

        char *ret = fgets(empName, 30, stdin);
        if (ret == NULL) {
                printf("Error while reading name\n");
                return 1;
        }

        // remove eventual trailing newline replacing it with '\0'
        empName[strcspn(empName, "\n")] = '\0';

        if (!(strcmp(empName,emp[1].name))) {      // 1
                // I don't know why you do this...
                strcpy(empName, "Steve xyz");
        } else {
                printf("Invalid name\n");          // 2
        }
}

edit: changed newline removal approach using strcspn() (thanks to @AndrewHenle in the comments) which seems to be a perfect fit for this task. from man strcspn:

size_t strcspn(const char *s, const char *reject);

calculates the length of the initial segment of s which consists entirely of bytes not in reject. returns the number of bytes in the initial segment of s which are not in the string reject.

fgets reads the characters from the input stream and also a newline character. So you need to remove the newline character from the empName and this can be done by:

empName[strlen(empName) - 1] = '\0';

#include <stdio.h>
#include <string.h>

typedef struct employee
{
    int cardNo;
    char name[20];
    long salary;
    int age;
} Employee;


int main()
{
    char empName[30];
    Employee emp[20];

    emp[1].age = 30;
    emp[1].salary = 7000;
    emp[1].cardNo = 1;
    strcpy(emp[1].name, "Steve xyz");
    
    int len = strlen(emp[1].name);
    emp[1].name[len] = '\n';

    printf("Enter your name\n");
    fgets(empName, 30, stdin);


    if (!(strcmp(empName, emp[1].name))) //1
    {
        strcpy(empName, "Steve xyz");
    }
    else
    {
        printf("Invalid name\n"); //2
    }
}

Tha fact is fgets() is reading also the \n char, so you have to do this after using fgets()

   size_t len = strlen(empName);

    if (len > 0 && empName[len-1] == '\n') {
        empName[--len] = '\0';
    }

With this we delete the \n, and now the comparison will determinate that are equals