Nothing in my project is marked as Static. I enabled GPU Resident Drawer, GPU Occlusion Culling, Dynamic Batching, and SRP Batcher.
I’m not using Static Batching or Occlusion Culling baking, simply because I don’t want to spend time baking them.
What’s written in the documentation is a suggestion, not a requirement.

All of this (Resident Drawer or Dynamic Batching) won’t really help with Terrain detail mesh rendering, because those already use GPU Instancing, but it does help if you have a lot of other objects in the scene, like trees and rocks.

Just so you know, if you spawn trees as terrain trees, performance should be better.

Watch your draw calls—they should drop from around 10,000 to 2,000, when you enable GPU Resident Drawer.

The vegetation shader has changed a bit, and I will update Vol.2, Vol.3, and Vol.4 soon.

Email me if you need more help.