Grafana 11.5.2: why cant i use "All" option in dashboard variable of "Data source" type?

I create a dashboard variable with type “Data source” and make sure in has “All” option:

The preview of values returns “All” among a bunch of individual datasources (they are all Elasticsearch type).

Then i create another dashboard variable $Deployment with type “Query” and make sure it references to the datasource variable that i created earlier:

Now, back in the dashboard when i set the $region variable value to “All”, i expect the $Deployment variable to contain all the the values from all the regions. But it doesnt happen - it displays only the values from the alphabetically first individual datasource.

Why is that? Is there any workaround?