If quantum computers are already in the hands of a bad actor and are able to crack Ethereum wallets (like using Shor’s algorithm) fast enough, it would be too late, since determining a bad-actor from the actual owner of the account wouldn’t be possible.
Do not use stateful post-quantum algorithms; rather use NIST standardized ones in hybrid mode (combiner) with a classical algorithm, like Dilithium + ed25519. Ethereum have to take a significant hit on block sizes though, due to the currently standardized post-quantum dsa scheme’s large signature and public key sizes.