Setup

Create a Rectangular Tilemap

Create in the scene

Remember to tick the static button at the top right corner

Change the name from "Tilemap" to "Placeholder"

Open Tile Palette and import your Tilemap Sprite

Create a TileLayer

Create

Fill all fields

It is recommended to separate your Tiles (For displaying) from a Tile (For placeholder)

Add TileGrid component and baking

Add the component to the root GameObject, not the Placeholder Tilemap

Config and baking