PG replicas and transactions atomicity

[Louis Laborde]

Are PG replicas updated atomically following the same transactions
boundaries as the source DB ?
For example, if 2 rows from a named table are updated atomically (with a
transaction) in the source DB, is there a guarantee that both
changes will be done atomically in a replica, or is there a time window
where only one changed row could be visible in the replica ?