where is the terrain …edit terrain layers button in unity 2019.3.12 … normally i would click paint texture and the edit terrain layer box would appear, in the earlier versions.
I’m having the same problem in Unity 2019.2.21f1
I was not having the of Edit Terrain Layer in unity 2020 (2021as well) at first. After a few research, I discovered that there is a section called Raise Or Reduce Terrain. If you click on it, a dropdown menu will appear, and one of the choices is Paint Texture.
Choose it. The Edit Terrain Layer will appear.
Same problem Unity 2020.3
I found the way to add the layers. I’m working in the HDRP, so maybe this is different.
Instead of seeing the button to edit layers when you select Paint Texture, I had to scroll down further in the Inspector, Below Target Strength.
In that is a Layers pulldown, and that has buttons to add layers for sand, moss, rock, etc. You can add layers for each, then select them to paint textures with the brush. Hard to find, but it is there.