I think it's accurate to say that the median American is insured, with only 8% of the population uninsured [1]. Although, to put that percentage in perspective, that's 26 million people and likely thousands in excess mortality relative to the insured poplulation.
I believe you're referring to the ACA's "individual mandate", which imposed a federal tax penalty for being uninsured. I won't argue whether that makes it illegal or not, but I can say that the individual madate was eliminated by the Tax Cuts and Jobs Act in 2019 [1]. There's no longer a federal tax penality for being uninsured.
[1] https://www.census.gov/library/visualizations/interactive/pe...