Anyway, to get somewhat back on topic, the safest wallet for you is going to be the one which protects best against the attack vectors which you deem most likely for you. If you honestly believe those attack vectors are from a three letter agency, then although a hardware wallet or encrypted airgapped wallet might prevent them from accessing your funds, you'll need to go to much greater lengths if you want to hide the existence of those funds altogether.
Only issue with super well hidden and anonymous funds, especially if there is no three-letter agency behind your ass: there will be a point in time where you'll want to spend those millions and then it may be hard to argue where that money came from. This is why I have this bookmarked:
You should never delete a wallet.
By keeping the private keys, you can always prove you just bought the
BTC in a point in time where you were able to afford them.
However, you'll have evaded wealth tax for years in case you lived in a country collecting such a tax. This might put you into jail.
So it's tricky to hold funds completely secretly, without landing in jail! Everyone should make sure to consider this.