How to carve/delete/erase out mesh.

It's... complicated. The term you're looking for is procedural mesh geometry.

The easiest way to do it is to use shaders. You can use stencils and depth testing to make any part of a mesh A inside a mesh B invisible, and only render the mesh B if it is inside the Mesh A. That allows you for example to have a hole inside a mesh. However, that won't help you with physics or large numbers of meshes.

Another way is to have tons of meshes that you delete, move or replace as needed. Think a simple version of Minecraft. This allows you to have apparently destructible buildings, but it's actually just a bunch of meshes losing their kinematic status.

Another simple way is the Terrain component of Unity. It allows you to load a bitmap as a terrain, and to update it inside the game using a few functions. Think sims-city or Cities Skyline.

The hard way is to calculate all mesh vertices that need to be deleted, all that need to be created, and update the mesh accordingly.

https://docs.unity3d.com/Manual/GeneratingMeshGeometryProcedurally.html https://www.reddit.com/r/Unity3D/comments/7gefbs/how_we_created_destructible_terrain_in_our_game/

https://youtu.be/9ZFM1H2qeYg

It's a little late, but it should help other people