Even in cases where the IdP supports both SAML & OIDC, I see almost no one choosing to use OIDC (a case of the devil you know?). The only real users of OIDC in an enterprise setting I see as a service provider, is G Suite businesses.
I'm pretty sure OIDC can be supported everywhere now. Okta, Oauth, PingIdentity, ForgeRock, Microsoft all support both. The last offender was Microsoft but it's included with active directory since 2016 both on premise or through Azure.
I'm working on auth for a big bank and it's definitely there, although not necessarily advertised and not everybody understand what is supported or preferred.
If a company were to only support OIDC nowadays, and maintain that OIDC is the preferred protocol when customers ask "can you do SAML?", I am willing to bet that most customers would integrate just fine either way.