Open Instagram on your browser; Login to instagram; Open your browser's console (CTRL + SHIFT + J); Paste the code below; Update the username in the first line; RUN IT (Hit enter)

getInstagramUsersThatDontFollowBack.js

const username = "USER_NAME_HERE";

/**
 * Initialized like this so we can still run it from browsers, but also use typescript on a code editor for intellisense.
 */
let followers = [{ username: "", full_name: "" }];
let followings = [{ username: "", full_name: "" }];
let dontFollowMeBack = [{ username: "", full_name: "" }];
let iDontFollowBack = [{ username: "", full_name: "" }];

followers = [];
followings = [];
dontFollowMeBack = [];
iDontFollowBack = [];

(async () => {
  try {
    console.log(`Process started! Give it a couple of seconds`);

    const userQueryRes = await fetch(
      `https://www.instagram.com/web/search/topsearch/?query=${username}`
    );

    const userQueryJson = await userQueryRes.json();

    const userId = userQueryJson.users.map(u => u.user)
                                      .filter(
                                        u => u.username === username
                                       )[0].pk;

    let after = null;
    let has_next = true;

    while (has_next) {
      await fetch(
        `https://www.instagram.com/graphql/query/?query_hash=c76146de99bb02f6415203be841dd25a&variables=` +
          encodeURIComponent(
            JSON.stringify({
              id: userId,
              include_reel: true,
              fetch_mutual: true,
              first: 50,
              after: after,
            })
          )
      )
        .then((res) => res.json())
        .then((res) => {
          has_next = res.data.user.edge_followed_by.page_info.has_next_page;
          after = res.data.user.edge_followed_by.page_info.end_cursor;
          followers = followers.concat(
            res.data.user.edge_followed_by.edges.map(({ node }) => {
              return {
                username: node.username,
                full_name: node.full_name,
              };
            })
          );
        });
    }

    console.log({ followers });

    after = null;
    has_next = true;

    while (has_next) {
      await fetch(
        `https://www.instagram.com/graphql/query/?query_hash=d04b0a864b4b54837c0d870b0e77e076&variables=` +
          encodeURIComponent(
            JSON.stringify({
              id: userId,
              include_reel: true,
              fetch_mutual: true,
              first: 50,
              after: after,
            })
          )
      )
        .then((res) => res.json())
        .then((res) => {
          has_next = res.data.user.edge_follow.page_info.has_next_page;
          after = res.data.user.edge_follow.page_info.end_cursor;
          followings = followings.concat(
            res.data.user.edge_follow.edges.map(({ node }) => {
              return {
                username: node.username,
                full_name: node.full_name,
              };
            })
          );
        });
    }

    console.log({ followings });

    dontFollowMeBack = followings.filter((following) => {
      return !followers.find(
        (follower) => follower.username === following.username
      );
    });

    console.log({ dontFollowMeBack });

    iDontFollowBack = followers.filter((follower) => {
      return !followings.find(
        (following) => following.username === follower.username
      );
    });

    console.log({ iDontFollowBack });

    console.log(
      `Process is done: Type 'copy(followers)' or 'copy(followings)' or 'copy(dontFollowMeBack)' or 'copy(iDontFollowBack)' in the console and paste it into a text editor to take a look at it'`
    );
  } catch (err) {
    console.log({ err });
  }
})();

this is great, thank you!

Great! And what if I want to automate the copy(followers) and copy(followings) commands? Is it possible to append to the same javascript code?

@AlphaC0de , that copy command is only for those that need to paste the data in a different program, such as a text editor. If you need to keep going with the automation (i.e., continuing the JavaScript code), you will have programmatic access to the followers and followings variables without doing anything extra... just access them and do whatever you need with the data.