Deforestation is the conversion of forest land to non-forest land.
The wood used for growing reishi is coming from tree farms which are continuously harvested and replanted. This is not deforestation.
The thing to remember with China is that they’ve had civilizations there for thousands of years. Much of China has been harvested many times over. What might look like wild foliage over there is almost certainly planted.
In much of our travels through China, we pass miles and miles of planted bamboo and hardwood lots. These areas are continuously harvested and replanted.
This is by no means similar to common contributors to deforestation like sugarcane, palm oil, rice, corn, and meat, where the forests are removed to produce these crops.