You already set up that workflow. That can be a major PITA.

Also I don't think this is as much about the "compute" of the background job as much as the nodejs app saying "take care of this for me please, got this? Don't bother me again until I ask for the result".

Endpoint handlers are flaky. They aren't guaranteed to run to completion even through no fault of their own. They should ideally have short and predictable run times, otherwise scaling is much more painful. That's why people separate out certain stuff into those background jobs. And getting that just right, scale it and so on can be quite a bit of work, but yes, something like Cloud Functions or Lambda would serve very similar functions. If you set up all the CI/CD pipelines to make that work.