At the moment the banks can create digits out of nothing if you lend money from them.
that's a myth, perpetrated by youtube videos and conspiracy theorists.
they don't just add digits, what is referred to as money creation by commercial bank is that money they lend out usually ends up as deposits at the same or another bank.
bank account balances are considered money, so if you depoit 100$ and they lend out 100$ to someone who puts it in his bank account, there are 200$.
the same thing could happen with bitcoins. bank account balances of a fractional reserve banking are nothing else than claims you have against the bank. but they are considered "money" by most definitions, so the base money supply is multiplied.