If Okta is the Identity Provider, how do I generate a Idp Signing Certificate for other SPs to use?

Just as the topic states … suppose I am using Okta as the Identity Provider and I have a separate SSO provider that is using Okta as the Identity Provider. Where do I find the info that contains the IdP Signature Certificate in Okta? Or is that something I need to generate?

https://developer.okta.com/standards/SAML/setting_up_a_saml_application_in_okta

You need to switch over to the Classic UI to get the screens shown in the doc. There will be a link that will be for the SAML IdP Metadata that you would use to configure the SAML SP.