As @Trevor Seward starts to explain - Azure AD Connect is not designed to work on Windows Server Core version - plus, this scenario will not be supported by Microsoft for production environment. As described on the following page : https://learn.microsoft.com/fr-fr/azure/active-directory/hybrid/how-to-connect-install-prerequisites.
Concerning Azure AD Connect, it's also not supported to have several Azure AD Connect for 1 Tenant / Azure Active Directory. Azure AD Connect is not really a SPOF but if you want to setup high-availability for this component - you may deploy 1 production and working Azure AD Connect + 1 another Azure AD Connect that will be configured in Staging mode. More details on this link part Staging server.