Same VPC, can't access postgresql of another host using EC2 psql

In the same VPC, I used CDK to create an EC2, a postgresql. I set EC2 as public, postgresql as private and allow all IPs to access postgresql default port Everything is ready, but can't telnet to postgresql using psql from EC2, anyone know the problem, am I missing something?

Vpc vpc = new Vpc(this,"RDS-VPC",
                VpcProps.builder()
                        .natGateways(1).maxAzs(2).build());

        SecurityGroup ec2SG = new SecurityGroup(this,"EC2-SG", SecurityGroupProps.builder().vpc(vpc).allowAllOutbound(true).build());
        ec2SG.addIngressRule(Peer.ipv4("xxx.xxx.xxx.xxx/32"),Port.tcp(22),"The specified IP can be accessed");
   
        SecurityGroup rdsSg = new SecurityGroup(this,"RDS-SG", SecurityGroupProps.builder().vpc(vpc).allowAllOutbound(true).build());

        rdsSg.addIngressRule(Peer.anyIpv4(),Port.tcp(5432),"allow public ssh access");
        List<SecurityGroup> securityGroups  = new ArrayList<>();
        securityGroups.add(rdsSg);
 Instance Ec2Instace = new Instance(this,"ec2", InstanceProps.builder().vpc(vpc)
                .instanceType(InstanceType.of(InstanceClass.T3,InstanceSize.MEDIUM))
                .machineImage(MachineImage.latestAmazonLinux(AmazonLinuxImageProps.builder().generation(AmazonLinuxGeneration.AMAZON_LINUX_2).build()))
                .securityGroup(ec2SG)
                .vpcSubnets(SubnetSelection.builder().subnetType(SubnetType.PUBLIC).build())
                .keyName("keyname")
                .build());
Credentials credentials = Credentials.fromPassword("xxx", new SecretValue("xxxx"));

        SubnetGroup subnetGroup = new SubnetGroup(this,"postgresql", SubnetGroupProps.builder().vpcSubnets(SubnetSelection.builder().subnetType(SubnetType.PRIVATE_WITH_NAT).build()).build());
        DatabaseInstance databaseInstance = new DatabaseInstance(this,"postgresql",DatabaseInstanceProps.builder()
                .vpc(vpc)
                .deleteAutomatedBackups(true)
                .instanceType(InstanceType.of(InstanceClass.T3,InstanceSize.MICRO))
                .allocatedStorage(10)
                .credentials(credentials)
                .databaseName("xxxx")
                .securityGroups(securityGroups)
                .subnetGroup(subnetGroup)
                .publiclyAccessible(true)
                .engine(DatabaseInstanceEngine.postgres(PostgresInstanceEngineProps.builder().version(PostgresEngineVersion.VER_13).build()))
                .build());