The category list was converted to a widget in Q2A 1.8, so it can be moved around on the sidebar. So if any custom themes override the sidepanel function you'll need to remove this line:
$this->nav('cat', 1);
For the Donut theme it's line 424 according to the GitHub repo.
Then you can add the category widget in Admin > Layout, and it will be the same on different themes.