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
How to get a year of FREE Nintendo Switch Online access via Amazon Prime
The Nintendo Switch paid online service doesn't sound great | Eurogamer.net
Nintendo Switch Online: Start Time and Signing Up
Nintendo Switch Online - Nintendo - Official Site
What's Included with a Nintendo Switch Online Subscription?
The Nintendo Switch's Paid Online Service Sounds Downright Bizarre
Nintendo Switch Online Expansion Pack Pricing Revealed - Game Informer
Nintendo Switch Online Membership Pricing And More Details Revealed - GameSpot
How To FIX " A paid membership to Nintendo Switch Online is required " on Nintendo Switch! - YouTube