JUNK MAIL
junk Mail? How do I see my junk folder? Literally I don’t have one!
When Apple ID is signed with account credentials from a web browser at www.icloud.com you can't create a folder named junk as inbuilt same named folder exists .
However , if you create a folder from mail application and name it as junk it will be created in iCloud section and mirrored in iCloud.com ( click on refresh icon it will appear ) .
Create or delete mailboxes in Mail on Mac - Apple Support