Not sure if this helps, but with @MADHOUSE’s solution, you can also go into the hierarchy tab on the left and ctrl/shift click there to select widgets, if there are many that are overlapping (making some hard to get at via clicking in the viewport).
However, that said, when you are in hierarchy view, you can’t use the arrow keys to nudge. If you want to get back into the designer window, simply clicking in there or clicking one element will deselect everything else, so just ctrl deselect one widget component, and ctrl select it back on again, and you’ll be able to nudge from there.
Apologies if I’m being Captain Obvious here. This solution just helped me move about 100 widgets into the right spot at the same time. Happy programming!