The answer
Seed length concerns entropy and backup format; it does not prove the chain uses a post-quantum spending signature. A long seed with classical elliptic-curve signatures may retain future quantum exposure.
What to do next
Check the signature algorithm implemented by consensus and how private keys are generated and recovered.
NIST Post-Quantum Cryptography resources
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Trezor hardware wallet
A current-generation hardware wallet for managing keys; it does not make Bitcoin or Ethereum quantum-resistant or resolve a future protocol migration.
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