Azure AD Premium still requires although I already have it in place

You are correct that an Enterprise Mobility + Security (EMS) E5 license includes Azure Active Directory Premium P2, which provides full coverage for Azure AD Connect requirements. According to Microsoft’s official documentation, EMS E5 bundles Azure AD Premium P2; however, Azure AD Connect itself does not require a separate Premium license. The service only depends on the appropriate features being enabled within the tenant. Therefore, if a license error is displayed, it typically indicates an issue with license assignment or provisioning rather than the absence of the entitlement.

https://www.microsoft.com/en-us/licensing/product-licensing/enterprise-mobility-security

https://www.microsoft.com/en-us/security/business/microsoft-entra-pricing

https://dynatechconsultancy.com/blog/comparing-microsoft-azure-active-directory-ad-premium-p1-and-p2-choosing-the-ideal-fit-for-your-needs