Per Bucket Monitor unable to display metrics

I have an OpenSearch Alerting monitor which is monitoring cpu usage of multiple hosts and raises an alert when the CPU threshold is breached. I want different emails for each host, that is why I’m using the per-bucket query - with hostname as bucket.
This way I’m able to get n mails for n different host threshold breaches with hostname as key in {{bucket_keys}} under {{ctx.newAlerts}}. Now in that mail I also want to publish the cpu usage data for each host.
How can I do that? Which variables should I access and iterate over?