3D world divided into grid cells

Hey guys, I am working on a demo for which I need to create a 3D game world.

The game runs on a grid system (players interact with cells to place objects etc).
Initially I started using the Unity Tilemap with 3D objects. However since the map will be quite large (300x300 tiles with a meassurement of 5x5 units each), I feel this might not be the best option performance wise.

I was wondering if it might be best to use the Unity Terrain tool to create the terrain and have a grid laid ontop of it, or do you have any other suggestions on what would be the best approach for this ?

My best approach would be to script a grid since if implemented right could give you the flexibility and freedom to modify, interact and implement other systems into it easily.

there are a ton of tutorials you can follow to achieve such a thing but if it proves too difficult you can look into other methods.