One of the HTTP/3 stream frames is called
PRIORITY. It is used to set priority and dependency on a stream in a way similar to how it works in HTTP/2.
The frame can set a specific stream to depend on another specific stream and it can set a "weight" on a given stream.
A dependent stream should only be allocated resources if either all of the streams that it depends on are closed or it is not possible to make progress on them.
A stream weight is value between 1 and 256 and it is specified that streams with the same parent should be allocated resources proportionally based on their weight.