Maybe my memory is faulty, but I never remembered having to pay a surcharge to use a credit card. Now everywhere I go there are signs saying that there is a 2.5-3.5% surcharge to use a car (and others that say that there’s a 2.5-3.5% discount for using cash, I assume to get around wording)
I work in fintech, serving the US market. Fees are varying but not specific to AMEX/Discover/MC/Visa. There’s card fees and then there’s gateway and payments processor fees. Often this is cumulatively just a flat fee, like $3-4, which is why some places will have signs saying “$3 extra charge for CC purchases below $20”.