~(이)라는 것은 is just ~(이)라는 with the word 것 (thing) and the topic marker ~은 after it. When you add ~(이)라는 to a noun, it has the meaning of “[...] that is called [...]” 것 is often used with ~(이)라는, such as 커피라는 것 (a thing called coffee), but other nouns can be placed after ~(이)라는 too, such as 슬기라는 사람 (a person called Seulgi). 것 is just frequently placed after ~(이)라는, it doesn’t add any actual nuance to it.