The current problem with ECDSA is that it is susceptible to attacks by quantum computer due to Shor's algorithm. This means that quantum computers can potentially crack ECDSA in a reasonable amount of time.
Shor's algorithm only provides quadratic speedup. That means that the approx. 256 bits of security of secp256k1 becomes approx 128 bits of security in a world of readily-available, at-scale quantum computing. I wouldn't call 2
128 brute-forceable "in a reasonable amount of time."
I think you're mixing up Shor's with Grover's.