Opera Next was rebranded Opera beta. (Because marketing.)

That is very unfrortunete. Have you got it up and running again?
If not you can reset the user profile to see if Opera will start-up then. To do that, please open a Finder window. In that window, press Command–Shift–G and type ~/Library/Application Support followed by Enter. Either delete or move the com.operasoftware.OperaNext folder somewhere else. (Even Opera beta’s folder is called OperaNext. Because engineering.) Try starting Opera beta again.