How to change page title of Manage Fields screen based on bundle name?
You need to replace the static title with a dynamic title.

Reference: https://www.drupal.org/node/2067859

This describes how to define dynamic titles for new routes in yaml files. You need to change the existing route entity.node.field_ui_fields in a route subscriber:

$route-&gt;setDefault('_title_callback', '\Drupal\mymodule\Controller\MyController::getTitle');


Reference: https://www.drupal.org/docs/8/api/routing-system/altering-existing-routes-and-adding-new-routes-based-on-dynamic-ones