I have my bitcoins in cold storage but I am using a read-only wallet with Electrum. Is that safe from hackers?
Yes. Your watch-only is safe because it does not store seed phrase, neither does it store any privacy key, only your master public key is stored which can not be used to access your Bitcoin. As the name denote, watch-only, it can not be used to sign a transaction.
I have an extended seed phrase, more than 12 words. Is it safe for future updates in the bitcoin network? Or is it possible that this feature will be disabled in the future so I can’t access my wallet anymore?
The 12 words are not extended words, it is the seed phrase. Store it very well as it will be required for wllaet recovery