If you uninstalled & reinstalled, you'll be using the default config now.
- How to create a Styles tab-bar (like Opus 9) may be what you're after.
The Explorer style only has one file display (and a folder tree) so I am not sure what you mean by "single file list", unless the style has been customized from its defaults (which shouldn't be the case if you just did an uninstall & reinstall, unless you have changed the config or imported a config backup, etc.).
- Turn on Preferences / Folder Tree / Options / Open second Folder Tree in dual display mode. You may also have to update the default lister (via Settings > Set As Default Lister), styles, layouts, etc. if you use them and they only open one tree.