I'm trying to find a Cadence metric that shows how many activities are waiting to be executed in a task list. Is there such a metric?
No, there is no a metric exactly like that. There have been several users asking for it but the architecture has made it difficult to support that.
Depends on what you really need, there are different approaches:
schedule_to_start_latency
on client metrics, or sync_match_latency
on server metrics.poll_no_task
on client metrics