Can a 51% Attack Steal Coins from Existing Wallets?

No, a 51% attack cannot steal coins from existing wallets by compromising private keys or creating new transactions. The attacker only controls the ability to confirm, reverse, or block transactions.

They can only double-spend coins they already possess. They cannot create new coins out of thin air or gain access to other users' funds, as those are protected by cryptographic private keys which the attack does not compromise.