Looking at the datamined info, the "Be a Chef! DIY Recipes+" Nook Miles redemption item (which unlocks cooking) is unlocked when you've upgraded Resident Services, K.K. Slider has visited and DIY customization has been unlocked.
You have to go to the Nook Mile Shop and buy the Cooking DIY recipe and then go to Nook Cranny's and go the cabinet that has a list of Cooking DIYS that you can learn.
Looking at the datamined info, the "Be a Chef! DIY Recipes+" Nook Miles redemption item (which unlocks cooking) is unlocked when you've upgraded Resident Services, K.K. Slider has visited and DIY customization has been unlocked.
Use inclines, bridges, fences, place furniture outdoors, plant trees, flowers and bushes. So, essentially, do basic stuff that increases your island rating.