Grafana 8.1.5 -> "OR" condition in alert not working as expected

I’m using Grafana 8.1.5
I have dashboard with Datasource as template variable.
I want to have alert on each Datasource_Dashboard > 0 metrics.
I cannot choose in the alert $Datasource (there is no such choice), so I’m trying to get all datasources into the alert and one expression for them all:

In the image you can see that there is no result from the query.
If I remove the “OR” condition this is what I get:

So, how come one datasource results with 1, but when I add “or” condition it results in NoData?
Isn’t this is exactly what “OR” statement should be all about, IF (A OR B == TURE) = TRUE?
Is there a better way to achieve that beside creating an alert for each datasource?