I created a Electrum wallet on my old machine (did not realise it was on v2.6) and transferred BTC to it from exchange. I did not realise at the time the wallet was not actually connected to servers. So the address I created and sent it to was never 'registered/published/requested' from blockchain I guess.
That's not a problem at all.
A transaction just
assigns BTC to a new address (technically not correct, but easier to understand this way).
Your address is derived from your public key which is derived from your private key. And the private keys of your wallet are derived from the mnemonic code (the 12 words).
So, as long as you have your mnemonic code, you are fine. An address does not need to be
registered. In fact, there wouldn't be any central instance where you even could register it.
I've not been able to get v2.6.4 to connect to any servers, and since realised the version it too old. I've had to install electrum on a newer PC, so I can install Electrum 4.0.4 which connects immediately.
But how can I re-create the receiving address in my new electrum wallet, and will i be able to retrieve the money I sent to that address?? Or is it lost?
Just use the
restore functionality with your seed/mnemonic code.