How can I use promql to create a panel on a dashboard? I want to create a query that I'm not able to do with the query builder and I wanted to try to make it using the promql builder, but I can't make it work with any query. Can I even use the promql builder when my metrics are being exported via opentelemetry?

I can only access the PromQL builder through Dashboard, it seems to be inaccessible from Metrics Explorer. You do have to use VERY CUMBERSOME syntax with quotes and braces, and that's documented here since it's a very recent change.

sum by ("k8s.cluster.name") (rate({"k8s.volume.available","k8s.cluster.name"="staging"}[5m]))

Thanks, I got it to work!