Calm Down.
Everybody needs to calm down.
Businesses are free, the seller, sets the conditions on how they do business in a free market.
“Legal Tender For All Debts, Public and Private” means just what it says.
You have not incurred an obligation or a _debt_ before you walk in a store, they are free to say “Only Circus Peanuts Accepted”, or Euro, Polish Zloty, or for the sake of argument, “Cash Only No Credit, No Checks”
See how that works? You haven’t bought anything yet. So there’s no debt.
Now let’s say you owe money - for taxes say, or a contractor. Cash is a huge PITA for businesses and government, but if they send you a bill they have to take it. Cash is legal tender for a debt, they may not like it, but they have to take it. In fact, if you offer to pay a debt with cash and they refuse, the debt is “extinguished”.
“You owe me $500”
“Here - take it.”
“Oh, I don’t take cash”.
“Sign here..” LOL
This is the reason people will push boundaries with dick moves like trying to pay property tax at 4 o’clock on Friday with all 1 dollar bills, or nickels, etc. It’s a gray area with coins. Usually after a lot of argument, coins will be accepted, but they must be rolled.