How would the hacker for example know my private key of an existing bitcoin address which stays connected only to my hardware wallet, is it possible for such address to be cracked from the hackers when the ECDSA is supposedly broken?
When you eventually spend some of the bitcoins that are stored in your hardware wallet, you will broadcast your public key to the entire world. The public key will be permanently stored in the blockchain for all to see for all of time.
Any outputs that don't get spent will then be vulnerable since they are still associated with that address and therefore with that public key.