Signature verification in Azure API Management with openid-config

I'm going through the documentation - https://zcusa.951200.xyz/en-us/azure/api-management/validate-jwt-policy to set up JWT validation for my APIs in Azure API Management.

What exactly are the steps executed when openid-config is included in the API Management Policy and an OpenID compliant configuration endpoint URL is specified? Is signature verification performed by default when openid-config is included?

Specifically, I want to understand when there would be a need to specify issuer-signing-keys and whether it is required if my OpenID compliant configuration endpoint URL provides the JWKS URI.