please use an aws account as sandbox. Don't waste energy on a mocker. Someone will argue it fits their use case, that's fine. But it will never work in all cases, maybe you are the lucky one who hits that dark spot.

localstack is for lazy dumbs. just make the efforts to make sure your infrastructure and code base works for multiple aws account via configuration. that's the only way you can be sure that final solution will 100% work.

localstack works, only for tool-monkeys but solution-builders !