Queue processors are leaking memory

Is this still applicable? If so, please provide clear steps to reproduce. I don't think it's related to system.module, the queue system is in core/lib/Drupal/Queue. I couldn't find a "queue system" component so I guess base system will have to do.

There's nothing to do. While leaking memory in long running PHP processes is, alas, all too frequent there is no need to be long running, the queue is perfectly fine to run one process for each item -- possible even in an parallel.

Probably something like Symfony Messenger + Drupal: Realtime Queues and Cron → is better for this anyway.

You can have the queue job running every 10 minutes (for example) and use the --time-limit=590 parameter for a new clean run. That way the queue will be continuously running but should not take too much memory. Change 10 minutes for whatever your memory threshold / time is.