On one of your page's components you attached either getStaticProps, getStaticPaths, or getServerSideProps as a member instead of as a separate export.

These methods can not be attached in the same way as getInitialProps and must be their own export

Move the method to it's own export from your page.

Before

function Page(props) {
  return <p>hello world</p>
}

Page.getStaticProps = () => ({
  props: {
    hello: 'world',
  },
})

export default Page

After

function Page(props) {
  return <p>hello world</p>
}

export default Page

export const getStaticProps = () => ({
  props: {
    hello: 'world',
  },
})

• Data Fetching Docs