Varies. Tether, in theory, is backed by dollar reserves. Bitcoin is created in exchange for services of validating the blockchain. I don't pretend to know how proof-of-stake and ther rest are created. But the existential nature of money is clear: if you can redeem it for stuff, it will trade as money, and you can only redeem it for stuff so long as the person you tender it to believes that the issuer will honor it in some common transaction, such as, for example, paying your mortgage or your taxes.

Thus, the whole question of "out of thin air" is a non sequitur. All money that is accepted in trade is accepted because someone will honor it. The money, then, is created "out of" - i.e., tokenizes - the credit of the issuer. The rest is metaphor.