So, i wanted to play ClassiCube but in single player and if you hit escape you can see an option named "generate new world" however that option is disabled. So, what I wanted to do next is to make a server myself. It is not very difficult. However, I'm a Mac user and all Programms I tried were made for Windows. I tought about 3 options. 1. Windows VM 2. Wine (converter for Windows programms for mac) and 3. ask the forum. So can I play alone or do I have to play with others / on a server?
Are you absolutely sure you weren't just trying to generate a map in multiplayer?
The button was not disabled when I tested in singleplayer (both 32 and 64 bit versions), and there's no code specific to the macOS build that would disable it.