Hi @Sewen - Welcome to AWS Quick Sight community and thanks for posting the question. Did you add Athena and S3 services from Quick Sight console. Can you please go to
Qucksight → Manage Quick Sight → Security & Permission → Quick Sight access to AWS services → select Athena and S3 and provide the require S3 bucket.
After doing it, please try to access Athena table, if possible share the screenshot as well.
Regards - Sanjeeb