When I go in Electrum to tab "Adresses" then I can select arbitrarily one of the green colored 34 char long addresses
(and tell it to the BitCoin sender).
Since Electrum has made native segwit the default address, I am surprised that you are still referring to legacy addresses which are 34 character long. Although nested segwit too are 34 character long.
Native segwit addresses (P2WPKH) are 42 character long.
This means that you have been using Electrum wallet for a long time ago. Either you generated the wallet long time ago when someone can click on legacy on Electrum to generate legacy addresses seed phrase or you used console for it which newbies will not likely think or know of.
There are reasons someone can be using legacy addresses, but know that with native segwit you can safe fee 42% more when sending from native segwit to native segwit addresses.
And there is no hidden (auto-)refresh of the available green addresses. All green addresses are hard linked to my wallet
and stay alive until I use them.
After receiving coin to an address, another address would be generated for you automatically. Just click on 'receive' on Electrum GUI to get it. If you need another address, click on receive on Electrum GUI, click on create request to generate new address for yourself. Those are your receiving addresses. I will advice you to use receiving addresses.
If you send bitcoin and you have change, it would be sent to your change address. Assuming you have 0.1 BTC UTXO received in a single transaction from Alice, and you sent 0.6 BTC to Bob, the change (0.4 BTC) would be sent to your change address on your wallet.
Although, you can also use change address as receiving address if you like.
Yes correct, all the green address are linked to your wallet, and you can use any of the wallets to receive your Bitcoin from your friend
Yes correct, all the green address are linked to your wallet, and you can use any of the
wallets addresses to receive your Bitcoin from your friend