Today I spent a long hour working out how to assign a lead to a queue in apex (salesforce).
You can't just assign it, you need go make a setup entry in the database first to mark the group as a queue.
But wait, you can't actually do that in the same context as making the group, so you have to make a subprocess, and mark it as a queue in that.

None of this is documented.
Screw you, SalesForce.