Re: "I can't log into my iCloud from my Mac Mini M4 (new)"
Your Apple Account is the account you use to access Apple services like the App Store, Apple Music, iCloud, iMessage, FaceTime, and more. It includes the email address and password you use to sign in as well as the contact, payment, and security details you use across Apple services.
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If you haven't already: You may need to sign in to your Apple Account online on your Mac mini M4. https://account.apple.com/
(If needed:
You can likely get a verification code to enter from another device (eg: iPad) that is already listed as a "trusted" device in your account, to enter on the Mac mini M4 to verify you are you..)
Once you have signed in to your Apple Account on the MacMiini M4 it will be listed as one of your "trusted" devices in your Apple Account. (It may take up to 24 hours to update everywhere needed.) Then you can likely log in to iCloud ok.