Can't set up a new Primary email account on my wife's Apple account.

The plonkers at Microsoft have decided to dump all hotmail accounts. Unfortunately my wife's email account was affected and we're trying to set up alternative email accounts, otherwise all her emails will disappear into a black hole and she will not be able to find them. Among the accounts she needs to amend is her Apple ID. At present, emails about the her iCloud data account are sent to her hotmail account. I'm trying to amend her primary email address to an iCloud email account which I've just created. Unfortunately the process described by Apple Support doesn't seem to work. I can sign into her Apple account, followed by Sign in and Security and then I tap edit next to the Email and Phone Number. Then my experience diverges from the instructions because when I tap on the remove button next to the hotmail address I do not get the delete button. Instead I get a box which says "Change your Apple Account" followed by a box which says "New Apple Account". When I insert her new iCloud email address in the box, and then hit the "Change Primary Email" button I get a message saying "If you make this change, you will no longer be able to use other email addresses as your account" which is fine as the only other email address she has is the non-functioning Hotmail account. Consequently I hit the "Continue button" and then I get a message in red saying "This email address cannot be used to create an Apple Account at this time" On another occasion I got an error message saying they couldn't create an account because the email address was an "alias", whatever that means. I don't understand all this rubbish because I don't want to create an account I just want to change the primary email.

Is my wife going to be excluded from her iCloud account forever because they insist on retaining an inactive email address? Has anyone any idea how I can resolve this issue?