How do I create a second iCloud email address on Mac mini?

Depends on what exactly you are trying to do.

You can log in to https://icloud.com/ and create an alias of your existing iCloud Account. Email sent to this alias will arrive at your current iCloud inbox but can be sorted into its own folder using mail rules if you want. To everybody else, this will look like it's own independent email address.

click here ➜ Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support

Or you can go to https://account.apple.com and create a completely new Apple Account with it's own associated iCloud email address.

click here ➜ How to create a new Apple Account - Apple Support

You cannot create just a standalone iCloud email address if that is what you mean.

While you cannot create a second, independent iCloud email address, you CAN create up to nine @icloud.com email aliases.

See this for instructions on how to do it -> Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support

Roy Bradshaw wrote:

Mac MiniM4 goldengate27.01.

how to make a second iCloud mail address

[Re-Titled by Moderator]

Original Title: second email address

I agree with Phil124 that an Alias of your primary iCloud account would be the easiest and best option.

The second option would be to get a Gmail account and add it to your Mail app.