Your code right now is returning the whole arr_2 because your filtering logic does not check if each item of arr_2 contains one of the matching strings in arr_1.

indexOf(arr_1) is essentially searching each item in arr_2 for the entire arr_1 array. The function will always return -1 because each item of arr_2 is a string and will never match with the entire arr_1 array.

I assume you'd want to go through each item in arr_1 as well, so you should probably do arr_1.forEach((item1) => { }) inside the forEach loop for arr_2, and do the indexOf check inside this inner loop.

You can't call indexOf on a string and pass an array as an argument.
You should use find to check if item has a domain from arr_1.
And it's a lot cleaner code using filter than forEach.

let arr_1 = ["domain1.com", "domain2.com"];

let arr_2 = [
  "domain1.com/about-us",
  "domain3.com/contact-us",
  "domain4.com/privacy-policy",
  "domain2.com/pricing-plans",
  "sub.domain2.com/home-1",
];

let filtered_arr = arr_2.filter(item => {
  return !arr_1.find(domain => item.includes(domain));
});

console.log(filtered_arr);

Note: This would also filter out "example.com/domain1.com".

you can achive it using filter some and includes

let arr_1 = ["domain1.com", "domain2.com"];

let arr_2 = [
  "domain1.com/about-us",
  "domain3.com/contact-us",
  "domain4.com/privacy-policy",
  "domain2.com/pricing-plans",
  "sub.domain2.com/home-1",
];

const arr3 = arr_2.filter(url => !arr_1.some(domain => url.includes(domain)))

console.log(arr3)