This is probably not relevant to some people, but I find that I'm always searching for this information when I need to print out a URL or find the current page path.
The difficulty is that finding or printing out a URL is very contextual and there is more than one way to get or use this information in Drupal. You might have a node object that you need to convert into a fully qualified path, or you want to print out the path of a route, each of which have different approaches. I think that's why there are so many questions asking variations of this topic on sites like Stackoverflow.
What is surprising to me is that there is very little documentation on drupal.org about this. Creating URLs and printing out links is perhaps the most common thing that needs to be done by developers creating themes, outside of changing the classes or markup of a block of HTML.
Read more here: https://www.hashbangcode.com/article/drupal-9-programmatically-creating-and-using-urls-and-links