This is quite a bit easier to accomplish than meat (as a product people want to consume). This is genetically modified yeast that produces cotton fibers. The same thing is done to produce insulin, and many other products.

Meat is far more complex though. It's not super difficult to grow meat, but it is in a form that resembles meat people expect and want. You can't just grow muscle. You need to have the correct ratio of fats, and not just the correct ratio, but it should be in the meat in an expected way, not just a seperate layer on top. It's complicated. It will be a huge benefit when it's available, but there are probably dozens of companies already working on it.