MXNB is the stablecoin behind your Mexican Peso balance on Moneda. In the app you simply see and hold a MXN balance. The stablecoin is the mechanism underneath, the same way EUR balances are held as EURC.
It is issued by Juno, a Bitso company that operates independently of Bitso. Juno is an authorised electronic payment institution under Mexico's Fintech Law.
What that means for you:
MXNB runs on Base, which is the network Moneda uses.
MXN is currently available to users in Mexico. If you do not see a MXN account yet, it may not be enabled for your account or country.