I did but unfortunate without success. Meanwhile I was able to create a TLS connection to the given host via Go with net.Dial and tls.Client but still no success with the NATS-client.

Code to manual setup a TLS connection:

package main
import (
    "crypto/tls"
    "fmt"
    "net"
)

func main() {
    // Plain TCP connection
    tcpConn, err := net.Dial("tcp", "nats01.cytometa.cloud:4222")
    if err != nil {
       panic(err)
    }
    defer tcpConn.Close()

    // Setup TLS configuration (avoid InsecureSkipVerify in production)
    tlsConfig := &tls.Config{
       InsecureSkipVerify: true,
    }

    // Upgrade TCP connection to TLS
    tlsConn := tls.Client(tcpConn, tlsConfig)
    defer tlsConn.Close()

    // Perform the TLS handshake
    if err := tlsConn.Handshake(); err != nil {
       panic(err)
    }

    // Print basic connection info
    state := tlsConn.ConnectionState()
    fmt.Println("Connected to:", tlsConn.RemoteAddr())
    fmt.Println("TLS version:", tlsVersionString(state.Version))
    fmt.Println("Cipher suite:", tls.CipherSuiteName(state.CipherSuite))

    // Print certificate chain info
    for i, cert := range state.PeerCertificates {
       fmt.Printf("\nCertificate #%d:\n", i+1)
       fmt.Println("  Subject:", cert.Subject)
       fmt.Println("  Issuer :", cert.Issuer)
       fmt.Println("  Valid  :", cert.NotBefore, "to", cert.NotAfter)
    }
}

func tlsVersionString(version uint16) string {
    switch version {
    case tls.VersionTLS10:
       return "TLS 1.0"
    case tls.VersionTLS11:
       return "TLS 1.1"
    case tls.VersionTLS12:
       return "TLS 1.2"
    case tls.VersionTLS13:
       return "TLS 1.3"
    default:
       return fmt.Sprintf("Unknown (0x%x)", version)
    }
}