Hi Ciaran,
Working with Nina in J4, the modules in side-column 2 doesn't come before (above) component in mobile view. Although I choosed in template > General > Responsive Options > Sidecolumn Positioning for 'Before Component'.
The (old) solution in https://www.joomla51.com/forum/sidecolumn-positioning-not-working-properly doesn't work.
Your elswhere given option @media only screen and (max-width: 840px) { .sidecol_b { order: 0 !important;} forces the right-column modules to the left – this is not what I want.
How to fix this?