But I am comming closer to the root of the problem. By renaming the server.ts file to server.tsx prettier runs as expected but I would like to keep .ts server-side.

Yes it is displayed in .ts files.

I have checked all extensions and I have only Prettier installed as a code formatter.

Thank you for your detailed explanaition. It really helped me a lot! I tried the better way like you suggested. I have setup an AppSync environment with IAM authentication settings. Also created a cognito user pool and an identety pool with 2 IAM roles, unauthenticated & authenticated and added the policies to the roles for accesing AppSync. { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "appsync:GraphQL" ], "Resource": [ "arn:aws:appsync:eu-central-1:135532242699:apis/cxa7cphbi5g5znie72o7rk7gde/types/Query/fields/getTask" ] } ] }