You can, and Carmine (who coded this update) wrote exactly about this on this blog post: https://paolino.me/solid-queue-doesnt-need-a-thread-per-job/

From his article:

One backend, two modes

Fiber mode isn’t universally better. CPU-bound jobs get nothing from it, and blocking libraries or C extensions that do not cooperate with Ruby’s fiber scheduler stall the reactor. And that’s fine – you don’t have to pick one.

As Trevor Turk pointed out in the PR discussion, that’s the whole point: separately configured worker pools. Here’s what Chat with Work actually runs in production:

workers: - queues: [ chat ] fibers: 10 processes: 2 polling_interval: 0.1 - queues: [ turbo ] fibers: 10 processes: 1 polling_interval: 0.05 - queues: [ notifications, default, maintenance ] fibers: 5 processes: 1 polling_interval: 0.2 - queues: [ cpu ] threads: 1 processes: 1