This is kinda a #fakenews comparison.
You can't just magically double the tax and replace employer subsidized insurance, which seems to be the inference from the OP.
As an aside the US spends roughly 16% of our GDP on healthcare which is about double what it was 50 years ago. We spend far above the next highest nation.
Magically, no...but Congress could pass a law that makes it happen. Or at least, a law that causes Medicare for All to replace employer subsidized insurance, with a tax rate approximately double the current 1.45%.
It would have to be determined through experience how close the new rate would be to exactly paying for the costs. Presumably if the variance is large, it would cause problems unless remedied, but that's different from requiring magic.
Fwiw, I assume the 1.45% employer share would also be doubled. So the total amount for expanded Medicare would be 5.8% of pretax wages. That's much less than 16% of GDP, but wouldn't be expected to cover all costs. It would only replace medical premiums, copays and some deductibles (I think), plus the portion of medical cost currently covered by employer sponsored insurance...will accept correction from those with more detailed knowledge, but a substantial portion of costs was excluded by OP's proposal.
Plus Medicare is sort of efficient, perhaps offering some savings rather than a mere redistribution of costs. Not magic, just efficiency from standardization, eliminating some of the numerous private sector middlemen, and freeing the patient from the need to pay for private sector profits.
So the proposal is plausible, maybe even realistic. Not magic, at least.