Yes, I think the only sense in which fiat is really "backed by govt" is the promise that it will be accepted by govt as taxes.
Discussion
Yup. Fiat gets its value because it’s the only way you can discharge your liabilities to the state. That’s what the Brits did in South Africa, imposing a ‘hut tax’ that could only be paid in British currency.
They don't even promise you that...