Probably a really silly question but what happens to crypto when quantum computing arrives?

With the seemingly compounding leaps and bounds we have been making in computing and ai technology, you can't help but think we may get quantum computing much earlier than we expected as a society.

Please be aware I know nothing about anything so will probably make dumb assumptions. Hypothetically someone builds a quantum computer that can crack the cryptography behind crypto and begins signing transactions from any wallet he wants to his own.

How long until crypto dies for good? Will we even notice what's happening at first? Is there anyway we could survive with some semblance of security? Will quantum computing even be able to crack seeds or sign other wallets transactions?

Again I don't fucking know anything so please don't shit on me until I die.