The following are the steps involved in accomplishing this in the most maintainable manner:
Use AWS CodeBuild with artifact encryption to replace the Jenkins instance running on EC2 instances.
Configure CodeBuild to encrypt the build artifacts using AWS Secrets Manager.
Deploy the containerized quality control applications to CodeBuild.
This approach is the most maintainable because it eliminates the need to manage Jenkins on EC2 instances. CodeBuild is a managed service, so the DevOps engineer does not need to worry about patching or upgrading the service.
https://docs.aws.amazon.com/codebuild/latest/userguide/security-encryption.html Build artifact encryption - CodeBuild requires access to an AWS KMS CMK in order to encrypt its build output artifacts. By default, CodeBuild uses an AWS Key Management Service CMK for Amazon S3 in your AWS account. If you do not want to use this CMK, you must create and configure a customer-managed CMK. For more information Creating keys.

EventBridge is needed to detect the database failure. Lambda is needed to promote the replica as it's in another Region (manual promotion, otherwise). Storing and updating the endpoint in Parameter store is important in updating the application. Look at High Availability section of Aurora FAQ: https://aws.amazon.com/rds/aurora/faqs/

The following are the steps that the DevOps engineer should take to reduce the latency of the Lambda function at all times of the day:
Configure provisioned concurrency on the Lambda function.
Configure AWS Application Auto Scaling on the Lambda function with provisioned concurrency values set to a minimum of 1 and a maximum of 100.
The provisioned concurrency setting ensures that there is always a minimum number of Lambda function instances available to handle requests. The Application Auto Scaling setting will automatically scale the number of Lambda function instances up or down based on the demand for the application.
This solution will ensure that the Lambda function is able to handle the increased load during the middle of the day, while also keeping the cold-start latency low.
The following are the reasons why the other options are not correct:
Option A is incorrect because it will not reduce the cold-start latency of the Lambda function.
Option B is incorrect because it will not scale the number of Lambda function instances up or down based on demand.
Option D is incorrect because it will only configure reserved concurrency on the API Gateway API, which will not affect the Lambda function.

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-importvalue.html
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-importvalue.html CF of network exports the VPC, subnet or needed information CF of application imports the above information to its stack and UpdateChangeSet/ ExecuteChangeSet

Amazon EC2 Image Builder is a service that automates the creation, management, and deployment of customized, secure, and up-to-date server images that are pre-installed with software and configuration settings tailored to meet specific IT standards. EC2 Image Builder simplifies the creation and maintenance of golden images, and makes it easy to generate images for multiple platforms, such as Amazon EC2 and on-premises. EC2 Image Builder also integrates with AWS Resource Access Manager, which allows you to share your images across accounts within your organization or with external AWS accounts. This solution meets the requirements of automating the tasks of updating the Linux AMIs, installing the Chef agent, and providing the images to the department's accounts with the least management overhead. Reference:
Amazon EC2 Image Builder
Sharing EC2 Image Builder images