S-class freighters are one of the rarest to be found in No Man's Sky; getting your hands on one takes a lot of patience.
That's how you get the best freighter in the S class! No Man's Sky Outlaws Gameplay
All ships and multitools are categorized by class in No Man's Sky, which determines the number of slots and bonus multipliers they can have. S-Class is the best you can get. They are very expensive and require a lot of time, as they are quite rare to find. If you want to own an S class freighter, make sure you have the money to buy the ship.
While there are many ways to obtain an S-class freighter, most are random. In fact, there is no guarantee that you will be able to find one.
You can usually face Freighters in space battles or Freighter battles. Fortunately, there is a way to make your S-class freighter easier to come by.