How to prevent Auto-deselect?

In Details Mode, when I click on a blank area of the file display, Opus deselects the files/folders automatically, how to prevent this behavior?

That´s by design, i would say. You could use the checkbox mode instead. Following code toggles the
checkbox mode & maintains your selection when toggling back:

@ifset: CHECKBOXMODE=Toggle Select FROMCHECKS Set CHECKBOXMODE=Off @ifset:else Select TOCHECKS

Use Power mode. Allowing you to change what the mouse buttons do is what Power mode is for.