This confusion arises naturally from the 1933 gold seizure.

FRN's are legal tender and can be redeemed by law in lawful money. So few people want to do so that the Treasury is okay with not printing more lawful money, which is currency in the form of cash US notes or gold.

You go to employers back and non-endorse the check redeeming it for lawful money.
You cannot do that. What you CAN do is demand lawful money. This is why I say (we say around here) that you get US notes in the form of Federal Reserve notes.

The rest is legal mechanism behind closed doors in secret. We presume that the bankers are making your non-endorsed funds special deposit, whenever you choose to deposit your paycheck instead of cash it.

And the bookkeeper can be king if the public can be kept ignorant of the methodology of the bookkeeping. All science is a means to an end.

The means is knowledge. The end is control. Beyond this remains only one issue; who will be the beneficiary. - from Silent Weapons for Quiet Wars by Hartford VAN DYKE.

Vicariously through the brain trust I have seen a bank branch shut down shortly after making demand that the suitors/redeemed have to stop non-endorsement.