Can't create Live account or login to my existing Live account

SAME SITUATION

I created a XBOX LIVE account for my son over a decade ago. I used my work email address when I created the gamertag. Back then Microsoft's services were not lumped under one login (that didn't even exist). When Microsoft deployed their one login system they
merged my son's Xbox Live account into my work Microsoft account.

Now my son is an adult. We need to transfer HIS Xbox Live gamertag to HIS Microsoft account.

This is idiotic.

-First you should create an xbox live account on your computer.

-Go to xbox.com - Log into your account.

-Once logged in select the "support" tab at top of page.

-Scroll a little and select "my account"

-After my account is selected, you can create an xbox live account, manage it or sign into it.

-Once your account is created you login to your profile on your xbox and then upload an already existing xbox live account.

-When it prompts you to enter a password after entering your email you may need to set an app password if your regular microsoft password doesn't sign you in.

To do so follow these instructions:

-Go to account.live.com and log into your microsoft account.

-Under "security & privacy" select "change password and more"

-Scroll down to "App passwords" and click "create new app password"

-This will generate an automated password that you'll see pop up on the screen.

Finally use this password to login to your xbox live account.

Hi! Can you kindly add a little more information to the question?

Are you trying to add an existing Xbox Live account to your Xbox 360?

If you are attempting to add an existing Xbox Live account to an Xbox 360, Create or go to the profile you would like the existing Xbox Live account to be accessible on, go to Xbox Live and download the existing account to the profile.

I just went through this with one of the kids accounts which is a free Live account and it does the same process. If her profile exists on the 360, she can't login to the One. Once it's removed from the 360, logging into the One is no problem.

I don't understand why we need an origin account, the case says "xbox live account" but nothing about anything else.. We can't get past the origin login screen to create a new account..