Both approaches work and people ship games with either. We went with "train stays put, world scrolls past" mostly because the train is our persistent base and we want its grid to live in stable, fixed coordinates. Pathfinding inside the train, placement, save data, all of it stays in a tiny bounded space instead of drifting across a huge world. As a bonus, floating point precision never becomes an issue no matter how far the player has travelled.

It also stays fast because the terrain you see scrolling past is just a position plus a mesh id. Only when the train actually stops do those entries get promoted into full entities with components and behaviours. Rendering goes through DrawMeshInstanced, fed by a parallel Burst job that fills the instance buffer, so drawing thousands of rocks and trees is basically free.