Answer
Rather than relying on a third-party LDAP-to-OpenID-Connect relay, bridging through Azure AD is the more established path: from Windows Server 2012 onward, you can subscribe to Azure AD and install Azure AD Connect on-premise to sync your existing on-prem AD users into Azure AD, then configure IFS Cloud to authenticate against Azure AD rather than your on-prem AD directly. This avoids needing to upgrade the underlying on-prem domain controller version just to get native OpenID Connect support, since Azure AD itself provides the OpenID Connect endpoint IFS Cloud needs.