ClickHouse.Client supports connecting to "managed" ClickHouse instances in Yandex.Cloud. As Yandex.Cloud has its own root certification authority, its certificate needs to be installed in system before one can connect to managed instance using SSL

Option 1: Certificate pinning

        private static bool ServerCertificateCustomValidation(HttpRequestMessage requestMessage, X509Certificate2? certificate, X509Chain? chain, SslPolicyErrors sslErrors)
        {
            // Hardcode or pass as parameter via currying
            const string YandexRootCAThumbprint = "AAA1450272071C2D8D7F48469886180B7685EF94";

            if (chain.ChainStatus.Any(status => status.Status != X509ChainStatusFlags.UntrustedRoot))
                return false;

            foreach (var element in chain.ChainElements)
            {
                foreach (var status in element.ChainElementStatus)
                {
                    if (status.Status == X509ChainStatusFlags.UntrustedRoot)
                    {
                        // If the certificate is not trusted from OS root, verify it matches expected thumbprint
                        if (element.Certificate.Thumbprint == YandexRootCAThumbprint)
                            continue;
                    }

                    return false;
                }
            }

            // Return true only if all certificates of the chain are valid
            return true;
        }

Option 2: Install Yandex certificate to truststore

Linux

sudo mkdir -p /usr/local/share/ca-certificates/Yandex && \
sudo wget "https://storage.yandexcloud.net/cloud-certs/CA.pem" -O /usr/local/share/ca-certificates/Yandex/YandexInternalRootCA.crt && \
sudo chmod 655 /usr/local/share/ca-certificates/Yandex/YandexInternalRootCA.crt

In RHEL, root certificates are located in /etc/pki/tls/certs/ instead

Windows

mkdir -Force $HOME\.clickhouse;
(Invoke-WebRequest https://storage.yandexcloud.net/cloud-certs/CA.pem).RawContent.Split([Environment]::NewLine)[-31..-1] | Out-File -Encoding 
ASCII $HOME\.clickhouse\YandexInternalRootCA.crt;
Import-Certificate -FilePath  $HOME\.clickhouse\YandexInternalRootCA.crt -CertStoreLocation cert:\CurrentUser\Root

See YCloud documentation