This pattern means "it is not that..." or "there is no guarantee that...". It is used to deny a general assumption or to state that something does not automatically follow. For example, if someone thinks that studying hard guarantees good grades, you can say 勉強すればいいというものではない (It's not that studying hard is all it takes). The nuance is that the situation is more complex or that other factors are involved.

You'll often see it in slightly formal or written contexts, but it's also used in spoken Japanese to make a reasoned argument. The phrase というもの is a nominalizer, and ではない negates it. You can also say というものでもない, which adds a nuance of "not necessarily" and is slightly softer.

Remember to attach to the plain form. For example, できる (can do) becomes できるというものではない. For nouns, like 学生 (student), it becomes 学生というものではない.