So far, the Electrum wallet has very high security, but when someone finds out your secret key it will be over because the wallet will immediately be drained.
If you are referring to security, know that it depends on how you use Electrum. Do not consider Electrum online wallet which is single signature wallet to have high security. But if you use Electrum on an airgapped device and not making it go online, it is highly secure.
It is not called security key but seed phrase. Or is it not seed phrase that you are referring to? Also worth mentioning that private key can be mentioned also because seed phrase that generates the private key or the private key itself should not be compromised as it will lead to lost of your coins.
I have hopes for the future development of Electrum, hopefully it will be equipped with 2FA layered security such as Google Authenticator or similar, when the secret key is leaked, there is still a second layer of security which still provides good security, considering that Bitcoin has top priority because the price is already very expensive, it is certain that many hackers will try to attack wallets that still have weaknesses like that.
Electrum has 2FA feature if you want to go for it, but the fee is huge and not encouraging. If you want an online wallet that is highly secure, why not just go for multisig on 2 or 3 devices.
Also know that you can add passphrase to your seed phrase to extend the words and anyone that do not know the passphrase but know your seed phrase can not access your wallet. But it has to be a very strong passphrase. Although , this does not mean you should show yourself seed phrase to anyone.