One thing to add:
The Timescale Cloud does allow you to do is create asynchronous read replicas across different clouds and regions (with a couple clicks).
You can then "fork" a read replica (at any point in time) and make it a primary to start serving out of that cloud (again, with just a couple clicks).
That's not quite the same as auto-replication/failover between clouds, but getting pretty far there.
Since TimescaleDB is also open-source, if you want that kind of replication scheme, you can always install on VMs across clouds. However, as you rightly pointed out, network latency is a definite concern and impacts the feasibility of RPO and RTO.