I guess its depends, for many use cases, it can be managed at application level. I've parted ways with FK for a long time since it created more hassles than it solved esp when it comes to sharding and replications.
You can always handle it at the application level.
The trick is that it's better to have the extra guard rails. And all of Couchbase, Yugabase, and Citus support foreign keys even with sharding and replication, so that's not an issue when the DB supports it.
