Update: this is still the case as of Renoise 3.2.2 (licensed) running on MacOS 10.15.5 Catalina.
When I enter fullscreen mode in Renoise (alt+enter), the MacOS Dock remains visible on the bottom, covering some of the controls. Normally for MacOS apps with fullscreen support, the Dock disappears completely as long as the app is in fullscreen. In order to access the Dock while in fullscreen, you need to use the mouse cursor to “pull down” below the bottom of the monitor for more than a second to trigger the Dock to reappear again.
You can work around the issue by using a second monitor or by exiting fullscreen mode when you need to access the area covered by the Dock, but that’s inconvenient.