As far as I know you can´t check it with either kubectl or kubernetes dashboard, it´s enabled by default as it´s just configuring envoy, which istio is based on.

I would say the easiest way to actually check if it´s deployed with istio is to create some simple envoy filter and try it. There are few examples in below documentation and in the tutorial.

As mentioned there and there

Istio uses an extended version of the Envoy proxy. Envoy is a high-performance proxy developed in C++ to mediate all inbound and outbound traffic for all services in the service mesh. Envoy proxies are the only Istio components that interact with data plane traffic.

Envoy is a high performance, programmable L3/L4 and L7 proxy that many service mesh implementations, such as Istio, are based on. At the core of Envoy's connection and traffic handling are network filters, which, once mixed into filter chains, allow the implementation of higher-order functionalities for access control, transformation, data enrichment, auditing, and so on. You can add new filters to extend Envoy's current feature set with new functionalities.

As mentioned in documentation there

EnvoyFilter provides a mechanism to customize the Envoy configuration generated by Istio Pilot. Use EnvoyFilter to modify values for certain fields, add specific filters, or even add entirely new listeners, clusters, etc.

Additionally take a look at this tutorial.

This should work kubectl get envoyfilter