Sadly, it doesn’t do anything. All preload does is move the file up the load order. It still doesn’t start until after the complete markup is received. Worse, it automatically makes the resource render-blocking as you’re literally saying “load this before the render starts”

Making it actually kind of pointless, since you can/should accomplish the same thing in most cases via code order.

I added a preload as=”style” for the screen.css to the live copy, zero change.

Just like how JavaScript is inherently single-threaded (making promises for anything other than load events utterly pointless) browser themselves tend to be when parsing the page. Until they make it multithreaded so that the parser can queue file downloads parallal to its own operation, that's not going to change.

More "legacy" that's just a pain in the ass.