How do they put this design in the wood?

sand the stain off after its engraved

It’s done with a CNC machine and then the design is burned with an iron.
It can also be done on a small scale with a router, but probably not as accurately or with as fine cuts and corners.

-- Improvise.... Adapt...... Overcome!

It looks to be cut using a cnc laser. As the laser passes over the grain of the wood where it’s more dense, the laser won’t cut as deep. The laser produces an intense beam which in turn burns/engraves the wood and leaves the surface charred. The intensity of the beam can be adjusted to either a shallow engraving or to cut through the wood. I’m not an expert on laser engraving/cutting but do have experience with it in one of my engineering courses.

-- Nathan