AWS Lambda times out when calling RDS Serverless

I have a VPC with two ISOLATED subnets, one for my RDS Serverless cluster, and one for my Lambda functions.

But my Lambda functions all timeout when they're calling my RDS.

My question is; is this VPC + isolated subnets a working structure for API Gateway -> Lambda -> RDS, or am I trying something impossible?

Lambda:

import * as AWS from 'aws-sdk';

const rdsDataService = new AWS.RDSDataService();

const query = `SELECT * FROM information_schema.tables;`;

export const handler = async (event) => {
  const params = {
    secretArn: `secret arn`,
    resourceArn: "rds arn",
    sql: query,
    database: 'db name'
  };
  const res = await rdsDataService.executeStatement(params).promise();
  return { statusCode: 200, body: {
    message: 'ok',
    result: res
  }};
};

My RDS and Lambda share a Security Group in which I've opened for ALL traffic (I know this isn't ideal) and my Lambda has a role with Admin Rights (also not ideal) but still only times out.

You are using the Aurora Serverless Data API. The API does not exist inside your VPC. You have chosen isolated subnets, which have no access to anything that exists outside your VPC. You will either need to switch to private subnets, or add an RDS endpoint to your VPC.