to make an interactive grid show up in single row view by default (like the selection "Single row view" in the row actions menu), put the following code into the attributes / settings of your PAGE (NOT your interactive grid), section JavaScript
> Execute when page loads
var ig$ = apex.region("StaticID").widget();
ig$.interactiveGrid("getActions").invoke("single-row-view");
Replace StaticID
with the StaticID of your interactive grid.
I know that this is old, but it was on top of my google search results, without the question being answered correctly.
I had the same question , and I have been searching the web for hours on how to accomplish this. And it's so easy, once you found it. ;-)
Kind Regards,
Nadine