Hi @Noëlla gabriël ,
>My question: if we run run the database that needs to be replicated in compatibilty mode 2016, can we than publish to 2012 subscriptors?
No, you cannot, because the version of the instance itself is SQL Server 2019, and two types of replication are contained in your replication configuration.
Actually in this case the compatibility level of the replicated database cannot determine anything. The version Backward compatibility of the replication topology refers to the SQL Server instance version. The component Publisher, Distributor, and Subscribers all acted by the database instances.
For merge replication, this topology is feasible: Publisher 2019 to Subscriber 2012. But for transactional replication, this is not feasible.
A Distributor can be any version as long as it is greater than or equal to the Publisher version (in many cases the Distributor is the same instance as the Publisher).
A Publisher can be any version as long as it less than or equal to the Distributor version.
Subscriber version depends on the type of publication:
A Subscriber to a transactional publication can be any version within two versions of the Publisher version. For example: a SQL Server 2012 (11.x) Publisher can have SQL Server 2014 (12.x) and SQL Server 2016 (13.x) Subscribers; and a SQL Server 2016 (13.x) Publisher can have SQL Server 2014 (12.x) and SQL Server 2012 (11.x) Subscribers.
A Subscriber to a merge publication can be all versions equal to or lower than the Publisher version which are supported as per the versions life cycle support cycle.
More details please refer to the doc Replication Backward Compatibility.