One successful quantum computer and all digital "security" as we know it ceases to exist.
Indeed it does, the issue is that successful quantum computer [for solving existing digital "security"] is always 10 years away, because guess what, size of keys for encryption is not staying in place, and growing qubit count of quantum computer is a task significantly trickier than slapping larger register on a CPU (which is not trivial task either).
Governments and banks can roll out new currency to replace the old if it becomes a risk for them
That's identical to saying existing currency will become scrap paper, not any different from crypto.
Indeed it does, the issue is that successful quantum computer [for solving existing digital "security"] is always 10 years away, because guess what, size of keys for encryption is not staying in place, and growing qubit count of quantum computer is a task significantly trickier than slapping larger register on a CPU (which is not trivial task either).
That's identical to saying existing currency will become scrap paper, not any different from crypto.