I made a slight modification to your bookmarklet asking to which instance you are migrating, which produces a list of links you can paste into something like https://www.openallurls.com so it becomes just a matter of clicking all of the “Subscribe” buttons:

javascript:(function() {
  const currentHostname = window.location.hostname;
  const tld = prompt("Please enter the name of the instance to which you are migrating:");
  const table = document.getElementById('community_table');
  const anchorTags = table.getElementsByTagName('a');
  const communityUrls = [];

  for (let i = 0; i < anchorTags.length; i++) {
    const title = anchorTags[i].title.substring(1);
    const parts = title.split('@');
    const community = parts[0].trim();
    const domain = parts[1] ? parts[1].trim() : currentHostname;
    const communityUrl = `https://${tld}/c/${community}@${domain}`;
    communityUrls.push(communityUrl);
  }

  const urlsText = communityUrls.join('\n');

  navigator.clipboard.writeText(urlsText)
    .then(() => {
      alert('Community URLs copied to clipboard!');
    })
    .catch((error) => {
      alert('Failed to copy Community URLs to clipboard:', error);
    });
})();