that's a comically archaic way of using the verb 'to be', not a grammatical error. you see it in phrases like "to be or not to be", or "i think, therefore i am"

that's a comically archaic way of using the verb 'to be', not a grammatical error. you see it in phrases like "to be or not to be", or "i think, therefore i am". "the feature isn't" just means it doesn't exist.