@m0ltar thank you for providing more clarity about the requirements. Please see below two links that guide you on how to setup Quick Sight to access data sources such as Redshift/RDS/S3 setup in another AWS account.
1/ Set up cross-account access from Amazon Quicksight to S3 | AWS re:Post
2/ Amazon Quick Sight deployment models for cross-account and cross-Region access to Amazon Redshift and Amazon RDS
3/Use Amazon Athena and Amazon QuickSight in a cross-account environment | AWS Big Data Blog
Let us know if this helps in solving your use case.
Thanks
Deepak