You should be able to hover over the warning symbol to see the exact definition query conditions that aren’t being met. I thought this feature used to exist — if it did, please bring it back!
As a workaround, I’ve been naming the definition query to match the exact conditions described in the query itself.
(using Pro 3.5.3)
Currently:

Only listing the definition query name isn't very helpful.
What my vision:

You can see exactly what definition query conditions aren't being met without having to open the layer properties 😁