var seq1 = new[] {"A", "B", "C"};
var seq2 = new[] {"1", "2", "3"};
var result = seq1.Zip(seq2, (x, y) => $"{x}{y}");

public static IEnumerable<R> ZipExact<T1, T2>(this IEnumerable<T1> source1, IEnumerable<T2> source2, Func<T1, T2, R> selector) 
{
    using var e1 = source1.GeEnumerator();
    using var e2 = source2.GetEnumerator();

    while(true)
    {
        var n1 = e1.MoveNext();
        var n2 = e2.MoveNext();

        if(n1 && n2)
        {
            yield return selector(e1.Current, e2.Current);
        }
        else if(!n1 && !n2)
       {
            break;
       }
       else
       { 
           throw new InvalidOpertaionException("Different sequence lengths");
       }
    } 
}