“The Congress shall have power...To coin money, regulate the value thereof,....”
Unless the Congress explicitly sets the value of a coin, it has no domestic legal value in my opinion.
A platinum Biden coin with One Trillion Dollars on it will have the market value people will pay for such a thing.
That would be true if we were bound by and following the Organic United States for America Constitution. Paper fiat is unlawful.
We are not, hence the rub. We are following the overlay Act of 1871 UNITED STATES of AMERICA constitution, where paper fiat is legal.
Legal is the undoing of Lawful.