Azure Bastion is a service that provides secure and seamless RDP/SSH connectivity to virtual machines directly over TLS from the Azure portal or via native client. Azure Bastion uses an HTML5 based web client that is automatically streamed to your local device. Your RDP/SSH session is over TLS on port 443. This enables the traffic to traverse firewalls more securely. To allow inbound access from the internet to Bastion1, you need to configure NSG1 to allow port 443 for the inbound security rule. Reference:
What is Azure Bastion?
About Azure Bastion configuration settings