Try no tls 1.3

.builder/actions/tls_server_setup.py

@@ -49,7 +49,7 @@ def run(self, env):
                                "-cert", "server.crt",
                                "-CAfile", "server_chain.crt",
                                "-alpn", "x-amzn-mqtt-ca",
-                               "-tls1_3",  # Allow TLS 1.3 connections only
+                               # "-tls1_3",  # Allow TLS 1.3 connections only
                                # "-verify", "1",  # Verify client's certificate
                                "-debug", "-state",
                                ], cwd=dir, stdout=subprocess.PIPE, stderr=subprocess.PIPE)