Ok, so more info on copying it over again, I am asked to retarget to .NET framework 4.8 - will this work?
I am trying again, having just rebuilt all, and then rebuilt individual project sections but I get an error that "this solution does not support individual rebuild etc" on some sections.
Still the toolbox is completely empty, "show all" shows all standard controls from Windows in grey, but no AHMI controls at all. No errors on rebuild all, including advancedHMIControls.