You need a paid membership to Nintendo Switch Online to play course world in Super Mario Maker 2. Pretty sure you could access course world at no extra cost in the original
Nintendo Switch Online - Nintendo - Official Site
Nintendo Switch Online Price And Features Revealed - Ougaming
Nintendo Switch Online 12 Month Family Membership | GameStop
What's Included with a Nintendo Switch Online Subscription?
Nintendo Switch Online + Expansion Pack Will Cost $50 Per Year - GameSpot