I would like to create a new @iCloud.com email account.

The Apple ID say example1@icloud.com can be created from a web browser at www.icloud.com see the article How to create a new Apple ID - Apple Support

This Apple ID as a mail address can be added in Mac system preferences > internet accounts , it will act as a mail account see some articles .

Use your Internet accounts on Mac - Apple SupportUse your Internet accounts on Mac – Apple Support

Change Internet Accounts preferences on Mac - Apple Supportsupport.apple.com › en-in › guide › mac-help › mac

Add an internet account - Apple Supportsupport.apple.com › guide › mac-help › mac

Toogood_22 Said:

"I would like to create a new @iCloud.com email account.: how do I do it?"

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About iCloud eMail Address Creation:

A. One iCloud eMail Address:

You can only create one iCloud eMail address. As an alternative, make an alias. That is how Apple has designed it. 

B. As an Alternatively, Use an Alias:

5 Aliases for an iCloud eMail:

You can have up to 5 aliases. Everything would be kept, but your eMail would be different. Trash all this junk, seeing if you no longer get it. You cannot turn off your current iCloud Account.  Go Here: Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support.