Add and remove custom user roles without plugin. Visit blog post https://bit.ly/3boczPg

custom_user_roles.php

<?php

  $msg = '';

  // Remove custom user role and assign all users with this role to subscibres.
  if (!empty($_GET)) {
    if (!empty($_GET['del'])) {

      $users = get_users(['role__in' => [esc_attr($_GET['del'])]]);  

      foreach($users as $user) {
        wp_update_user([
          'ID'   => $user->ID,
          'role' => 'subscriber'
        ]);
      }

      remove_role(esc_attr($_GET['del']));

      $msg = "Custom user role removed!";
    }
  }

  // Create new custom user role and assign selected caabilities.
  if (!empty($_POST)) {
    if (!empty($_POST['user-role-name']) 
      && !empty($_POST['user-role-caps'])) {

        $user_role = esc_html($_POST['user-role-name']);

        foreach($_POST['user-role-caps'] as $idx => $val) {
          $user_caps[$val] = true;
        }

        $result = add_role(
          strtolower(str_replace(' ', '_', $user_role)),
          $user_role,
          $user_caps
        );

        if (null !== $result) {
          $msg = "New <strong>{$result->name}</strong> user role created!";
        }
        else {
          $msg = 'Custom user role already exists!';
        }
    }
  }

  // Add UX to the Settings page to create and delete custom user roles.
  add_action('admin_init', function() use($msg) {

    add_settings_field('manage_custom_user_roles',
      'Custom User Roles',
      function() use($msg) {

        global $wp_roles;

        // Load FA and customize the multiple select dropdown with checkboxes.
        wp_enqueue_style('fontawesome-4.7', 'https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css', null, false, 'all');
        wp_add_inline_style('fontawesome-4.7', '
          .select-checkbox option:not([value=""])::before {
            content: "\2610";
            width: 1.5rem;
            text-align: center;
            display: inline-block;
            height: 1.5rem;
          }
          .select-checkbox option:not([value=""]):checked::before {
            content: "\2611";
          }
          .select-checkbox-fa option:not([value=""])::before {
            font-family: FontAwesome;
            content: "\f096";
            width: 1.5rem;
            padding: .5rem 0;
            display: inline-block;
            margin-left: 2px;
          }
          .select-checkbox-fa option:not([value=""]):checked::before {
            content: "\f046";
          }');
        ?>
        <div class="roles">
          <!-- UX section to remove/delete user role -->
          <?php foreach($wp_roles->roles as $role => $attrs) :?>
              <?php if (!in_array($role, ['administrator','editor','author','contributor','subscriber'])): ?>
                <p><?php echo $attrs['name'];?> <a href="?del=<?php echo $role;?>">[x]</a></p><br />
              <?php endif; ?>
          <?php endforeach;?>
          <!-- Output message -->
          <p>
            <strong><?php echo $msg;?></strong>
          </p>
          <!-- UX section to craete new user role -->
          <p>
            <input type="text" name="user-role-name" id="user-role-name" size="40" required />
          </p>
          <br />
          <select class="form-control select-checkbox-fa" multiple size="25" name="user-role-caps[]" requierd>
            <option value="export">export</option>
            <option value="import">import</option>
            <option value="read">read</option>
            <option value="">-----------------------------------------</option>
            <option value="delete_others_posts">delete_others_posts</option>
            <option value="delete_posts">delete_posts</option>
            <option value="delete_private_posts">delete_private_posts</option>
            <option value="delete_published_posts">delete_published_posts</option>
            <option value="edit_others_posts">edit_others_posts</option>
            <option value="edit_posts">edit_posts</option>
            <option value="edit_posts_role_permissions">edit_posts_role_permissions</option>
            <option value="edit_private_posts">edit_private_posts</option>
            <option value="edit_published_posts">edit_published_posts</option>
            <option value="publish_posts">publish_posts</option>
            <option value="read_private_posts">read_private_posts</option>
            <option value="">-----------------------------------------</option>
            <option value="delete_others_pages">delete_others_pages</option>
            <option value="delete_pages">delete_pages</option>
            <option value="delete_private_pages">delete_private_pages</option>
            <option value="delete_published_pages">delete_published_pages</option>
            <option value="edit_others_pages">edit_others_pages</option>
            <option value="edit_pages">edit_pages</option>
            <option value="edit_pages_role_permissions">edit_pages_role_permissions</option>
            <option value="edit_private_pages">edit_private_pages</option>
            <option value="edit_published_pages">edit_published_pages</option>
            <option value="publish_pages">publish_pages</option>
            <option value="read_private_pages">read_private_pages</option>
            <option value="">-----------------------------------------</option>
            <option value="delete_themes">delete_themes</option>
            <option value="edit_theme_options">edit_theme_options</option>
            <option value="edit_themes">edit_themes</option>
            <option value="install_themes">install_themes</option>
            <option value="switch_themes">switch_themes</option>
            <option value="update_themes">update_themes</option>
            <option value="activate_plugins">activate_plugins</option>
            <option value="delete_plugins">delete_plugins</option>
            <option value="edit_plugins">edit_plugins</option>
            <option value="install_plugins">install_plugins</option>
            <option value="update_plugins">update_plugins</option>
            <option value="">-----------------------------------------</option>
            <option value="create_users">create_users</option>
            <option value="delete_users">delete_users</option>
            <option value="delete_users_higher_level">delete_users_higher_level</option>
            <option value="edit_users">edit_users</option>
            <option value="edit_users_higher_level">edit_users_higher_level</option>
            <option value="list_users">list_users</option>
            <option value="promote_users">promote_users</option>
            <option value="promote_users_higher_level">promote_users_higher_leve</option>
            <option value="promote_users_to_higher_level">promote_users_to_higher_level</option>
            <option value="remove_users">remove_users</option>
            <option value="">-----------------------------------------</option>
            <option value="bulk_edit_roles">bulk_edit_roles</option>
            <option value="create_roles">create_roles</option>
            <option value="delete_roles">delete_roles</option>
            <option value="edit_role_menus">edit_role_menus</option>
            <option value="edit_roles">edit_roles</option>
            <option value="list_roles">list_roles</option>
            <option value="">-----------------------------------------</option>
            <option value="level_0">level_0</option>
            <option value="level_1">level_1</option>
            <option value="level_10">level_10</option>
            <option value="level_2">level_2</option>
            <option value="level_3">level_3</option>
            <option value="level_4">level_4</option>
            <option value="level_5">level_5</option>
            <option value="level_6">level_6</option>
            <option value="level_7">level_7</option>
            <option value="level_8">level_8</option>
            <option value="level_9">level_9</option>
            <option value="">-----------------------------------------</option>
            <option value="delete_attachments">delete_attachments</option>
            <option value="delete_content_shortcodes">delete_content_shortcodes</option>
            <option value="delete_login_redirects">delete_login_redirects</option>
            <option value="delete_others_attachments">delete_others_attachments</option>
            <option value="read_others_attachments">read_others_attachments</option>
            <option value="">-----------------------------------------</option>
            <option value="edit_attachments">edit_attachments</option>
            <option value="edit_content_shortcodes">edit_content_shortcodes</option>
            <option value="edit_dashboard">edit_dashboard</option>
            <option value="edit_files">edit_files</option>
            <option value="edit_login_redirects">edit_login_redirects</option>
            <option value="edit_nav_menu_permissions">edit_nav_menu_permissions</option>
            <option value="edit_others_attachments">edit_others_attachments</option>
            <option value="edit_widget_permissions">edit_widget_permissions</option>
            <option value="">-----------------------------------------</option>
            <option value="manage_capabilities">manage capabilities</option>
            <option value="manage_categories">manage_categories</option>
            <option value="manage_links">manage_links</option>
            <option value="manage_options">manage_options</option>
            <option value="">-----------------------------------------</option>
            <option value="moderate_comments">moderate_comments</option>
            <option value="unfiltered_upload">unfiltered_upload</option>
            <option value="update_core">update_core</option>
            <option value="upload_files">upload_files</option>
          </select>
        </div>
        <script>
          // Allow to have multiple selects without the need of CMD or CTRL keys.
          (function($) {
            $('select.form-control option').mousedown(function(event) {
              event.preventDefault();
              $(this).prop('selected', !$(this).prop('selected'));
              return false;
            });
          })(jQuery);
        </script>
        <?php
      },
      'general',
      'default',
      array('label_for' => 'manage_custom_user_roles')
    );
  }, 10, 1);