You are confusing Shors and Grovers algorithm. Shors algorithms is for cracking vulnerable asymmetric encryption algorithms, it is able to do so extremely quickly with a sufficient amount of qubits. Grovers algorithm is for cutting symmetric algorithm key strength in half, making 128 bit encryption as strong as 64 bit, and 256 as strong as 128. Using 256 bit symmetric algorithms is considered quantum resistant, an RSA key with comparable quantum resistance would be too big to fit on most hard disks according to one paper I read on the subject.