Xcode 26 does seem to eliminate the + icon in the window titlebar. Oddly, when editing a storyboard, the + for the Objects library was moved to a new location in the bottom-left corner of the storyboard editor area. But there's no corresponding moved + icon when editing code.
The "Editor" | "Create Code Snippet..." menu does open the snippets window without creating a new snippet as long as there's no current text selection.
Right-clicking in the code editor includes a "Create Code Snippet..." context menu but doing that does add a new snippet in addition to opening the snippet window because, annoyingly, right clicking in a code editor always selects something as the context menu appears.
The simplest solution would be to assign a hotkey to the "Create Code Snippet..." shortcut. Go to Xcode -> Settings -> Shortcuts. In the Shortcuts pane, enter "snippet" into the search (filter) field. Click in the empty area to the right of the "Create Code Snippet..." shortcut. This activates a text field where you can enter your desired shortcut. Enter something like Ctrl-Option-S or whatever you like.
Now while working on any code, type the hotkey you set and the snippets window will appear. The only caveat is that you want to ensure you have no selected text when you enter the hotkey. If there's any selected text when the hotkey is typed then the snippet window will open with a new snippet added for the selected text. If you do this by mistake, it's easy enough to delete the new snippet.