Can Microsoft JDBC Driver 4.0 connect to SQL Server 2019 and perform DML without issue? The SQL version compatibility BOL article advises that the minimum compatible JDBC driver version for SQL Server 2019 is 7.4.
Can an older JDBC driver still connect to SQL Server 2019? Or can only the driver versions listed as compatible connect to the specified SQL Server versions?
Microsoft and my testing have confirmed that JDBC drivers not marked as compatible in the SQL version compatibility matrix might connect to a non compatible version of SQL Server and continue to work without issue.
 
However, there is no guarantee that all functionality detailed in the Driver feature support matrix for Microsoft SQL Server is supported. They also only test the  driver versions marked as compatible against the stated version of SQL Server.
JDBC version 4.0 was not specifically tested.