JavaScript Bookmarklet for the WordPress classic editor which enables mastodon publishing (assuming you have at least one mastodon publishing account enabled under https://jetpack.com/redirect/?source=jetpack-social-connections-classic-editor / https://wordpress.com/marketing/connections/)

enableMastodonPublishing.js

javascript:(function(){
  publicizeFormEditHref = document.getElementById('publicize-form-edit'); // "edit" href
  if(publicizeFormEditHref) {
    publicizeFormEditHref.click();
  }
  mastodonCheckboxes = document.getElementsByClassName('wpas-submit-mastodon'); // any Mastodon checkboxes (one can have zero or more accounts configured)
  Array.from(mastodonCheckboxes).forEach((mastodonCheckbox) => {
    mastodonCheckbox.checked = true;
  });
  publicizeFormHideHref = document.getElementById('publicize-form-hide'); // "OK" button disguised as href
  if (publicizeFormHideHref) {
    publicizeFormHideHref.click();
  }
  savePostButton = document.getElementById('save-post'); // button exists when post has status "draft"
  if (savePostButton) {
    savePostButton.click();
  }
  else {
    updateButton = document.getElementById('publish'); // button exists when post has status "draft", "scheduled", or "published"; when "draft" a click() will either "schedule" or "publish" depending on the schedule timestamp being in the future or past
    if (updateButton) {
      updateButton.click();
    }
  }
})();