Async secondary replica can receive the log from primary replica in SQL Server 2017 on Linux. However, it does not harden or redone.
You can query last_redone_lsn and last_redone_time from sys.dm_hadr_database_replica_states on secondary replica to check whether it is progressing or not.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
This issue is fixed in the following cumulative update for SQL Server:
About cumulative updates for SQL Server:
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server:
To work around this issue, you can use one of the following methods:
Pausing and resuming the data movement on secondary replica will make the pending changes applied.
Restarting SQL Server on secondary replica will also make the pending changes applied.
Learn about the terminology that Microsoft uses to describe software updates.