Drupal 9: Programmatically Creating And Using URLs And Links
Philip Norton, Hash Bang Code Ltd., Mar 20, 2022
https://www.hashbangcode.com/article/drupal-9-programmatically-creating-and-using-urls-and-links
Not the best quick look-up but an excellent deep dive into the URL, URI, and Request objects.
Creating Links in Code for Drupal 8
David Valdez, Agaric, Apr 14, 2017
https://agaric.coop/blog/creating-links-code-drupal-8