"ID Token Signing Algorithm" (idTokenSigningAlgValues) option has been added to the "OpenID Connect Provider" (com.liferay.portal.security.sso.openid.connect.internal.configuration.OpenIdConnectProviderConfiguration) System Settings interface. Defaults to "RS256". When "Discovery Endpoint URL" is set, Liferay is fetching the required metadata about the provider including this information from the provider.
Please update Authenticating with OpenID Connect guide with this information. (Mention in "Configuring an OpenID Connect Provider Connection".)