Metrics not useable in reports

In metrics on Kibana 7.9.1 is it possible to add additional metrics to alert on past the default CPU, Memory, Load, traffic rate and log rate?

For instance adding system.filesystem.used.pct shows the metrics as expected. Saving the settings and making them default will put it up correctly every time you come back to the page.

Click Alerts, create alerts then move down to the "When select a metric" and you will not have the options past the defaults above.