I’ll pass along the libertarian solution from Dr. Mary Ruwart and her “Cliff Notes” for “Healing Our World”, a blog post called “How to create enough wealth to retire the national debt, keep our promises to seniors, and more!”.
Much of what she proposes is reducing government services, or people’s dependency on them, so that privately held wealth increases. Translate: privatize “Social Security” completely. (Chile sets an example.) But what I recall from Harry Browne’s books in the 1990s was admission that promises to some seniors in one generation would have to be broken (by sudden means testing) to fix the problem. I even recalling this point coming up an LPVa convention in Manassas VA in, as I recall, May 1996.