Explorer Replacement and Desktop double-click are not part of the Light version. Light vs Pro
dopusrt.exe isn't involved in Explorer Replacement (intercepting folder requests from Explorer), only Desktop double-click. If dopusrt.exe isn't running then I would expect Desktop double-click to not do anything, at least related to Opus. (Maybe there's some confusion about what Desktop double-click is as it should not blank any icons. Desktop double-click means double-clicking an empty area of the desktop to cause Opus to open a window or do some other action.) There is at least one other program which can do things when you double-click on the desktop (one of the multi-monitor tools, if I remember correctly), so you might be triggering that instead.
How to stop the Opus image viewer from being used by default