That isn't one of the default/standard commands (unless you mean toggling the Folder Tree, which is in the Lister menu with F8 hotkey by default).
If you were using a customized toolbar/menu setup before, it's still there and you can switch back to it or temporarily turn it on to copy custom buttons out of it as needed: Your toolbars are still there after you upgrade.
in what sense? Could you give an example? The default toolbars between Opus 11 and 12 did not change fundamentally; we just added some new commands to them. If the Opus 12 toolbars seem unfamiliar to you, maybe you were not using the Opus 11 toolbars either but have a setup dating back to a much older version? You can always go back to your old toolbars if you wish.
Please post a screenshot so we can see how the filter is set up and some examples of files shown that shouldn't be.
PS/Reminder: please ask one question per thread.