Thanks for your response. I may be confused about terminology--in the documentation I see the term "lister" used for a single file window panel rather than the entire (in my case four-panel) window. In any case...as the attached screenshot illustrates, on your recommendation I locked both individual panes the way I want them, then saved the layout as "startup."
Then I confirmed in preferences that on startup launching from Desktop, Opus should open that layout, "startup." Then I close Opus, restart it, and it unfortunately shows the bottom layout, with both panels in detailed view and locked.
Somewhat surprisingly, when from that point I manually open the saved layout "startup," it displays the way I want it, with the top lister in list view, and the bottom one in detailed view. So it seems like it is not opening the "startup" saved layout on startup, despite that setting in preferences.
I also tried "set as default lister," your other recommendation, with the same result. Whichever lister is active the last time I do this, is the way both listers display when I relaunch Opus. In the screenshot shown here, I set the bottom lister as default lister last, after doing the same with the top lister. If I set the top list as default list last, then on launch it would show both in "list" view.
Thanks for you attention. I hope I can figure this out.