"AWS SDK for Java 1.x end of support" caused by AWS CloudWatch Logs Insights activity

Yes, this is plausible. The user agent string you're seeing in CloudTrail indicates that AWS's internal services are using AWS SDK for Java 1.x version 1.12.797. When you use CloudWatch Logs Insights through the AWS Console, the backend AWS services that process your query may be using SDK v1 internally.

This is AWS's internal usage of the SDK, not your application code. The end-of-support notification you received is specifically about YOUR use of AWS SDK for Java 1.x in your own applications and code. You should not be concerned about AWS's internal service usage - AWS will handle migrating their own internal services.

The notification is meant to alert you if you have applications or code that directly depend on AWS SDK for Java 1.x. Since the SDK entered maintenance mode on July 31, 2024, and will reach end-of-support on December 31, 2025, you should focus on migrating any of your own applications that use SDK v1 to SDK v2. If you're only seeing this SDK usage from AWS Console activities and not from your own applications, then you likely don't need to take action regarding your own code.

To verify, check if any of your deployed applications, Lambda functions, or other code directly uses the AWS SDK for Java 1.x dependencies.
Sources
General Availability Release of the Migration Tool for the AWS SDK for Java 2.x | AWS Developer Tools Blog