I have set the following two options, but I can’t see Metric Alerts at the alert page.
How to enable Metric Alert?
Which version of Sentry is this?
21.1.0
These are the changes needed to enable metric alerts: feat: Allow metric alerts to be used in on-prem by wedamija · Pull Request #735 · getsentry/onpremise · GitHub
Very likely you have the changes in the docker-compose.yml file already as you are using 21.1.0 so you just need to update your config file and restart your instances.