Is it cost effective to provide free healthcare to the citizens of a country regardless of age and pre-existing conditions?

Theoretically it is possible to care for your citizens. Britain has been doing it since 1948 !
There are queues. Delays. Shortages. But we do get seen ! We do get treated.
There's no profit in people. And that's the first lesson you have to learn.
Not every child you treat for a life threatening illness will go on to become a chemist or a research scientist ! Not every pensioner who gets a new kidney will devote their lives to a worthy cause to better mankind.
People are expensive to maintain. Another fact you have to get used to.
One of the tings you need to do is abolish ALL insurance policies !!
Those companies are sucking you dry to please shareholders !!
So you need a National Insurance underwritten by government.
I know everybody hates taxes but there it is. And if you don't see good healthcare as a worthy thing worth your tax dollars, well, maybe you live a charmed life !!
Something else you could do is nationalize a major drug research company.
That way, any new drug you create could then be sold worldwide ! Pumping your money back into the drug company to expand it's research and development.

If these shitters were non-profit then we could probably standardized the industry and have to spend less on hiring people that only deal with insurance companies in the HC industry. But that's not the americunt dream.

What there should be is limits to corporate healthcare greed, but you won't hear politicians talk about that, the healthcare industry bribes all of them, Rep and Dem.

By "free" do you mean "free at point of service" or "no premiums"?