Hi Per Axel,
From what you described, it would be the Hide My Email address that gets verified, not your personal iCloud one to which the email was forwareded.
To learn more about this feature, check out the link here: What is Hide My Email?
Hide My Email generates unique, random email addresses that automatically forward to your personal inbox. Each address is unique to you. You can read and respond directly to emails sent to these addresses and your personal email address is kept private.
*If you create an account with an app or visit a website that supports Sign in with Apple, you can choose to share your email address, if you're familiar with the app or website, or hide your email address, if you'd prefer more privacy. If you choose the Hide my Email option, only the app or website you created the account with can use this random email address to communicate with you. Learn more about Sign in with Apple.
*With an iCloud+ subscription, you can generate unique, random addresses on your device with iOS 15, iPadOS 15, or macOS Monterey or later in any email field in Safari. You can also generate email addresses on-demand in the Settings app in iOS or iPadOS, in System Settings or System Preferences in macOS, in the Mail app, or on iCloud.com. In iOS 16 or iPadOS 16 or later, you can also keep your email address private in third-party apps. Learn more about iCloud+.
Apple doesn't read or process any of the content in the email messages that pass through Hide My Email, except to perform standard spam filtering that's required to maintain our status as a trusted email provider. All email messages are deleted from our relay servers after they're delivered to you, usually within seconds.
At any time, you can change the email address that receives forwarded messages. Or you can choose to turn off email forwarding to stop receiving messages. You can manage your addresses created with Hide My Email in Settings in iOS or iPadOS, System Settings or System Preferences in macOS, or on iCloud.com.
We recommend the article above because it will explain in more depth how Hide My Email works.
Please do not hesitate to contact us if you have more questions.
Thanks for using the Apple Support Communities.
Cheers!
