It's supposed to be automatic unless you opt out, but AFAIK the article doesn't tell you how to do that. Maybe a new W-4 form?
I suppose it's also automatic for Social Security recipients unless they opt out. The ones who have dementia will probably have the amount deducted automatically, and also won't know how to make a claim, so it will probably collect money for the government, but the govt. will spend many times the amount it collects.
Just looked at some summaries and it seems that retirees and unemployed MAY sign on.
If retired sign on, it is going to come out of SS benefits, near as I can tell.
I suspect we will be inundated with policies designed under this act as soon as the zero signs it.