AG listener with MultiSubnetfailover True on Named Instance
As HandyD stated - the official doc does not mention issues with named instances. I also have not experienced any issues with AO multi-subnet failover with named instances.
The SQL Shack article to which you linked states: &quot;It does not support SQL named instances. We can connect named SQL instances using a SQL listener&quot; (emphasis added).  I think the confusion is caused by poor choice of words.  I suspect what the author meant to say is that in order for multi-subnet failover to work, a listener must be used to connect, using the instance names to connect will not work.