Lots of applications and sites (particularly SPAs or sites with lots of data to load such as YouTube) have a progress bar that is displayed at the very top of the screen.
Does this have a special name?
According to Material.io, these UI elements are called progress indicators:
Progress indicators inform users about the status of ongoing processes, such as loading an app, submitting a form, or saving updates. They communicate an app’s state and indicate available actions, such as whether users can navigate away from the current screen.
That's a progress indicator.
I think Flickr might be the first one start using this in early days, that will be back at least 10 years ago, then Material design release an official doc and usage for this.
Sitepoint called it "Progress Loading Line".
Which seems like specific, "progress indicator" is general term.