Using an alias emal
Is it possible to always use my alias email address in icloud, Or is it timed to be deleted at some point
iPad Pro (3rd generation)
It's possible to use email address in iCloud see Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support
Note: You cannot delete or turn off a primary iCloud Mail address. You cannot use an alias to create a separate Apple ID, and an email alias cannot be converted to a primary iCloud Mail address.