So basically using multi-Sig cold wallet on airgapped machine provides the ultimate security?
Using multi-sig in one machine makes little sense. Multi-sig provides extra security, provided that transactions are signed in multiple devices.
If an address is multi sig of say 3 address then attacker has to find 3 private keys correct?
If the address is a 1 of 3 multi-signature address, a single private key would be enough.
Important to mention that an attacker needs the two other public keys as well, in contrast with single-sig, wherein just having the private key is enough to move the money.