X / Twitter is not providing a list of “not follow back”. If you want to check the loyalty of the people you’re following, you can (on a computer):

1. Open https://twitter.com/your_user_name/following page on Chrome.
2. Press F12 (or other shortcut) to open dev-tools
3. Go to console tab and paste the code at the bottom of this article
4. type hideNF(5) in console tab, press enter

This will hide the accounts that followed you back, so you can decide what to do for those who didn’t.

async function hideNF(n) {
  while (n--) {
    fdivs = document.querySelectorAll('[data-testid="cellInnerDiv"]');
    fdivs.forEach(function(e) {
      isF = e.querySelector('[data-testid="userFollowIndicator"]');
      if (isF != null) {
        e.style.display = 'none';
      }
    });
    await new Promise(r => setTimeout(r, 1000));
  }
}