Alice has a debt to Bob.  For Bob that's an asset, for Alice that's a liability.

The denomination of the debt has a backing.  That can be fractional or full, or, psychological.

Full or fractional reserve debt can be done with either bitcoin, gold, or any bearer instrument.

But each of these things has an addressable market, and practical limits on what size of that market it can occupy.

Yes it can be done, but it's complicated.