All prime numbers other than 2 are odd. Yet the vast majority of odd numbers are not prime.
E.g take the primes 3 and 5, their product is 15 and can be used as an (insecure) RSA modulus. 15 is an odd composite number.
Composite means it has multiple prime factors.
Natural numbers greater than 1 are all either prime or composite.
For secure RSA we use much larger primes. But the principle is the same We multiply to large odd primes and get a large odd composite modulus $n$.
Finding the factors of such a large composite can be very hard. In some cases beyond what is currently possible. But hard to factorize doesn't mean the factorization doesn't exist. And in fact with the help of the private key it's even easy.
So impossible to factorize might mean, not practical even by a nation state spending a billion dollars. With this definition RSA 4096 is impossible to factorize.
But if you mean impossible as in not possible, even with unlimited compute, or a futuristic quantom computer. Than all RSA moduls are composite and thus possible to factorize.
P.s - factorize might be defined to allow "factorization" of primes, which is easy just detect that it is prime, using e.g Miller-Rabin and if so return a list containing only the input number.
