If you did it during 2021 and you literally copied your seed from the blockchain wallet to Electrum and protected the same wallet with a strong password, then it is unlikely that someone hacked you with the help of a seed. The only thing that comes to mind is that maybe you did a malicious Electrum upgrade, although you didn't mention it.

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The very fact that you had 2 wallets with the same seed means that you were exposed to a double risk, although an online wallet is always a much higher risk due to phishing, hot desktop/mobile are also not immune to a malicious wallet upgrade that gives the hacker complete control over your coins.

We have all been warned about such things, the only question is who received this information and how seriously they took it.

Electrum vulnerability allows arbitrary messages, phishing
Reminder: do not keep your money in online accounts