performance – Is grass object amount limited in Unity?

I’m using Unity 2019.3.7f1 free version to create a small game project. I have a large terrain which I want to fill with grass. To achieve that I’m using the grass brush tool provided with the terrain.

However I cannot put more than, say 10’000 grass items (arbitrary, I don’t know the real limit). Exceeding this amount, the grass objects contained in the first area I filled are removed, one by one, for a reason I cannot figure out. It’s like there is a max limit of grass object I cannot exceed, and this is true for both grass textures and detail meshes.

On the other hand the amount of tree seems unlimited, which is puzzling me.

So my questions are:

  1. Is there a limited amount of grass objects available in Unity?
  2. If yes, how many grass objects are available, and may I increase this limit?
  3. Is it a known bug, or a known limitation of the Unity free version?
  4. May grass impact the global performances of the game? (I feel that my game is significantly more slow after I added the grass…)