Reference to Security Group from another VPC

Question

Improved Question: Scenario:

I have two VPCs: vpc1 and vpc2 connected through an established VPC peering connection. A service runs within vpc1 and needs to access an RDS database in vpc2.

Goal:

Grant secure access to the RDS database in vpc2 from the service in vpc1 solely using security groups.

Current Approach:

Vpc:

const securityGroup = new ec2.SecurityGroup(this, 'mysg', {
  vpc,
});

const fargateService = new ApplicationLoadBalancedFargateService(this, 'MyService', {
  cluster,
  taskImageOptions: {
    ...,
  },
  cpu: 512,
  memoryLimitMiB: 1024,
  taskSubnets: {
    subnets: vpc.selectSubnets({ subnetType: ec2.SubnetType.PRIVATE_WITH_NAT }).subnets,
  },
  loadBalancer: lb,
  certificate,
  securityGroups: [securityGroup],
});

VPC2:

    const mySG = ec2.SecurityGroup.fromLookupByName(
      this,
      'DbAccessSecurityGroup',
      'PlatformServiceSecurityGroup',
      legacyVPC // vpc1
    );
    const dbSecurityGroup = new ec2.SecurityGroup(this, 'DbSecurityGroup', {
      vpc,
    });
    dbSecurityGroup.addIngressRule(mySG, ec2.Port.tcp(5432), 'Allow access');

    new rds.DatabaseInstance(this, 'mydb', {
          ...,
          securityGroups: [dbSecurityGroup],
});

VPC peering is already setup in another stack

Is it possible to achieve this solely using security groups, or are there any other recommended approaches for secure communication across VPCs?