Is there a compatibility mapping Istio - Kubernetes - couldn't find one. Istio 1.7 release notes mention needs K8s 1.16+, but nothing with Istio 1.6 or Istio 1.8
Support status of Istio releases is what you looking for.
For istio 1.9 you can use Istio Prelim 1.9 website
These steps require you to have a cluster running a compatible version of Kubernetes (1.16, 1.17, 1.18, 1.19). You can use any supported platform, for example Minikube or others specified by the platform-specific setup instructions.