If you get the following error when trying to run some Terraform:

error creating Appstream Fleet (): InvalidRoleException: AppStream 2.0 encountered an error because your service role 'arn:aws:iam::<ACCOUNT_ID>:role/service-role/AmazonAppStreamServiceAccess' is invalid

..then you just need to run your IaC again, as the roles are automatically created when you first interact with the service.

Alternatively, go and have a look at what has already been created in the AWS Console.

What roles are required for AppStream?

Role required by AWS AppStream:

Learn more about the roles required here:
Roles Required for AppStream 2.0 and Application Auto Scaling