WalShadow requires direct access to the physical WAL, and most managed Postgres providers don't allow that. It works with ClickHouse Managed Postgres or self-hosted Postgres. I talk about this in the blog:

Physical WAL is key to WalShadow’s architecture, but most managed Postgres services don’t expose it to customers, making it impossible to use WalShadow. ClickHouse Managed Postgres manages both sides of the stack, allowing us to integrate WalShadow directly into the Postgres replication layer and provide a native path from Postgres WAL to ClickHouse.