Since upgrading to Win 10, Windows file operation windows (e.g., Save, SaveAs), etc no longer contain a DO file tree but default to the horrible Windows defaults. How do I ensure that the file tree on the left side of ALL windows uses the DO structure.All Windows Integration options are checked except Add 'Open in Directory Opus' items to folder context menus, which is grayed out.
My DO version is 11.x (I could be more specific but there's no about or help option that I can find in DO -- another flaw.)
At least on the standard Operations toolbar in Opus 12, at the extreme right there is a Help button (which also contains a question mark). One of the choices from clicking that button is About Directory Opus.... I think that was also true in Opus 11, but am not certain,
Opus has never affected what you see in the common file dialogs (Open/Save/etc). Windows 10 changed some things around in how the tree is displayed but that's entirely a Windows 10 issue, and has nothing to do with Opus.
You can check the program version using the Help -> About command (as @rcoleman1943 says).