Welcome to the forums. That's strange, maybe you just lost the icon to access the app drawer.
There are different ways to open the drawer with Nova:
- Swipe up from the dock. Depending on your Nova settings there could be a little arrow over the dock (Nova settings - app & widget drawer - enable swipe to open).
- Widget. Long press an empty spot on your home screen - select 'widgets' - drag 'Nova actions' to the home screen - select 'app drawer'.
- Gesture (only available on Nova Prime). Set a gesture to open the drawer in Nova settings - gestures and input - select a gesture - set as 'app drawer'.