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
What you need to know about the new Nintendo Switch Online + Expansion Pack membership plan. - News - Nintendo Official Site
How to Redeem Nintendo Switch Online 3 Month Membership Code - YouTube
Nintendo Switch Online - Nintendo - Official Site
Nintendo Switch Online membership: what you need to know | TechRadar