If you're using the databricks terraform provider, make sure the role's name matches the instance-profile name.

If not, use the `iam_role_arn` attribute to explicitly set the role's arn when creating the databricks instance profile

resource "databricks_instance_profile" "this" {
  instance_profile_arn = aws_iam_instance_profile.this.arn
  iam_role_arn         = aws_iam_role.this.arn
}

 In addition to adding the databricks serverless role to the trust policy as others have stated above.