put the draw rectangle back into the standard and advanced toolbar
put the rectangle tool back into the toolbars
There was a bug which allowed to accidentally drag-n-drop tools and insert them into other tools’ subgroups.
It was fixed by introducing a special mode to enable this. No accidents with lost tools should happen. Please comment back if it happens for you in latest versions.
The Rectangle Tool is there already but may be hidden depending on what you selected in the tool bar. You may have selected another shape, like the circle tool, that occupies the same icon, but is a fly-out menu of alternate shapes.
Now if that is not what you are experiencing, if you want a perfect Square, use shift to constrain, otherwise rectangles are what you will produce, thus to add another button to do what the current one already does would be redundant and a waste of space.