Can not change Apple ID to alias
I need to change my Apple ID to one of my aliases since I created it a long time ago and now this strange Apple ID is showing up when sending people an calendar invite :(
Changing the Apple ID to an alias should be possible as per https://support.apple.com/en-au/HT202667
However, when I try to do so I can only choose to change my main Apple ID to the variants of @me.com, @mac.com and @icloud.com but not the several other aliases (of course with @me.com, @mac.com and @icloud.com) I have.
My aliases are all available under https://www.icloud.com/mail/
What am I doing wrong?