Maybe this is a user error issue, but I do not see any way to resize panes when I have multiple notes open when in sliding panes view. Dragging the cursor over the border between the notes does not produce a resize pane cursor. I am still able to resize the sidebars when they are open, though. I seem to remember this function existing in the past with the sliding panes plug-in.
Mac OS Monterey 12.5 (Macbook Air M2)