The new materials Basalt, CrackedLava, Glacier, Ground, Mud, Sandstone, and Snow all display in the properties window for regular BaseParts. These can be applied to any BasePart, but the object will just turn invisible. These materials should be hidden from the properties pane just as water is.
Or howabout you make all the terrain materials usable on baseparts (would love a Water basepart…)
Oh, I know what the problem is (I think). I overwrite new studio versions with a custom reflectionmetadata that has folders, unions, and negations displayed in a better order + de-clutters the advanced objects window. The reflectionmetadata xml must be really outdated by this point, which is why the new materials aren’t explicitly told to be hidden. Sorry to trouble you 