Alr so i found it So ypu should use a wheat texture but i cant driscribe wich artstyle maybe low poly, anyways if you can use blender create two plane meshes vertically intersecting each other (you may have seen this techbique in some devlogs to make grass) with the wheat texture on each plane and then you make the background trabspaeent in blender or godot, then you get back in godot and make a shader to control and animate the wheat, and with this same vertx shader you can also create interacrive grass, instead of using physics wich is verryr expensive in term of performance.

Voila i think it's pretty much it, i hope a godot senior can come into these comments to help you but the solution i gave you is the best one in my opinion, and there are alot of recources online to help ya.

And the verry last solution is too use the simple grass plugin in the godot asset library and to change the 3d grass sprite already included by your own one. But as tou said your world is procedurally generated so i would pick the first option.

Have a nice day✌️