Part of my workflow was to isolate a layer/group and then export it by itself. Today, however, I upgraded
to Krita 3.1 and now exporting an isolated layer doesn't work. When I export, it exports the entire image
as if I hadn't isolated anything at all. Was this intentionally removed? Is there a work around other than
manually hiding all other layers one by one before exporting the parts I want?

I haven't verified this, but it sounds like a regression. Please file a bug for it.