How can you express (1234) in S4 as a product of disjoint cycles? In S4, how would you express (1234) as disjoint cycles?
I did try almost every possible case (12)(34) or (13)(24)   (14)(23)
none of these mathces with 1234

As noted in the comments, $(1234)$ is already a cycle and hence is a product of disjoint cycles. Product is perhaps used a bit loosely here, but by most definitions an element standing alone is a product with $1$ factor, and a product with $0$ factors is usually defined to be the identity element. This is just something to get used to, and most would agree that these definitions are useful because in many cases we avoid having to treat $1$ and $0$ differently.
For example, the fundamental theorem of arithmetic says that every positive integer is a product of primes. This includes prime numbers, which are products of $1$ prime, as well as $1$, which is a product of $0$ primes.
