These feature appears to be available now in the new Adobe. Go to Menu > Preferences... (or Ctrl+K) > General > UNcheck the box "Open documents as new tabs in the same window (requires relaunch)" > scroll down and click OK.
If you don't see the option, make sure you have the latest version of Adobe available by going to Menu > Help > Check for updates.

Why did they break this long-standing functionality? I NEVER want PDF documents to open in tabs in the same window! How can we disable this "new" interface now? The old method and options don't seem to be available any longer.

Why would you remove this simple yet important feature? Please bring back the ability to open documents in separate windows.

Please again provide an option in Acrobat Reader DC and other "new UI" products to force separate windows, instead of tabs.

Microsoft Excel designers once decided to change to tabs instead of separate windows. After endless complaints, they had to go back to separate windows.

(Yes, I know that we can revert to the "Classic" interface, at least for now. And yes, I know that we can drag a tab to create a separate window, clumsily and at a waste of time. Neither "feature" is equivalent to having the original option to open a separate window for the document by default (i.e., except when a pdf is being dragged into an existing window).)

Why has this been changed. In earlier versions it was possible to select in the settings whether to open new pdf in one window or in separate windows.

Adobe Acrobat 2023 ("New Acrobat") needs the option to open each document in a new window.

This should be possible without disabling New Acrobat.

Why was this feature removed?? I can't stand having everything open in tabs under one window. I also need to have the ability to have separate windows for my docs!