Adding a custom SAML or OIDC app in Azure AD

Is the following assumption correct? And if so, what is the rationale behind the different approach?

When adding a custom SaaS application using saml, you need to create a service principal (through the Enterprise Application blade), Azure also creates an application object in the background.

When adding a custom SaaS application using OIDC/oauth, you need to create an application object (through the App registrations blade), Azure also creates a service principal in the background.

Thank you!