I tested this scenario and it seems if vacuumdb is started with multiple jobs and one of the jobs doesn't complete due to a lock or whatever reason, other jobs will stay idle and don't release the connection until the stuck job is finished.
For my understanding, why do we need this behaviour?
I don't think we **need** this behavior, it is just a simple way to wait for each one to finish and then close it; waiting for each specific one in the order it is present in the list. Is there an important reason we need a more complex behavior, closing each one as soon as it becomes idle once the work queue is empty?