We're facing the same problem, this would be awesome to have fixed.

Our case:

1. We have tags on the task definitions (tags on all resources as part of our IaC)
2. As part of our Github Actions workflow, new container images are being built, pushed to ECR and the task definition updated.
3. The tags for the task definition are gone, even after trying the new propagate tags feature.

We have had this same problem for a couple of years now and are using a custom composite action to download the task definition including tags. It does look like though the v3 ecs client can do this with the correct inputs:
https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/ecs/command/DescribeTaskDefinitionCommand/

const input = { // DescribeTaskDefinitionRequest
  taskDefinition: "STRING_VALUE", // required
  include: [ // TaskDefinitionFieldList
    "TAGS",
  ],
};

It'll have to be added somewhere in the params here: https://github.com/shesaave/amazon-ecs-render-task-definition/blob/master/index.js#L61

I do believe this is being worked on in #325