You just need to add one line "preferCSSPageSize: false,". It will make your code as

await page.pdf({ path: FILENAME,

format: 'A4',
margin: {
    top: "0px",
    right: "0px",
    bottom: "0px",
    left: "0px"
},
printBackground: true // required for photos otherwise blank
preferCSSPageSize: false,

});