Sure, You can compare Cloud SQL vs Cloud Spanner and RDS vs Dynamo, but it makes more sense to just say "Postgres" and assume that the reader can figure out that it means "Whatever managed postgres service you want to use".

The entire point is that every cloud provider has a managed postgres offering, and there's no vendor lock-in. Though, technically, Dynamo does have a docker image you could run in other cloud providers if it came down to that, you'd get no support for it.