Unity 2020.2.2f1, MM2 2.1.2
When following along with the Objects tutorial (https://youtu.be/q36sPkKz6-8?t=861) I noticed that the generators for trees cannot be disabled. You can flip the enabled/disabled options in the right-click menu but the objects remain in the scene. It's also the same for Grass.
Removing the connection for the Trees serves as a workaround but this does not work with the Grass output. I haven't tried other outputs yet.