Ability to disable login field in SSO Registration Form

From what It has been told me, is not currently possible to disable login field in the customer SSO registration form.

https://community.lithium.com/t5/Developer-Discussion/Disable-login-field-SSO-Registration-form/td-p/442420

Is it possible to do so ?

Because the strange thing is that I have already passed the login value in the SSO Cookie, but when the user get redirected to the SSO registration form, the login field form is enabled and is blank.

Does it suppose to be filled with the login value specified in the SSO cookie, or not ?

Thanks