Alby Account (getalbycom) and Alby Extension both need to be connected to some lightning node. The default and soon only node will be users own Alby Hub, after we replace custodial shared node down.
You can connect Alby Account to some node (like Alby Hub), to use lightning address of that Account with your node. You can customize the node in "Wallet configuration" on getalby.com/node
For each Account, you can freely customize your lightning address in Settings.
Nostr identity is a separate story: you can use your Nostr keys in the extension (independent from your Account), and you can set up NIP-05 identifier to specific npub on your Account (getalbycom).
Then, the extension can independently have many wallets, each of them managing one nostr key and one lightning node interface / wallet.
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We know it's challenging, but freedom to link/unlink and customize comes with responsibility ;)
Happy to help further!
PS Feel free to come join our cal.com/getalby/alby-hub-onboarding to grasp it all quickly! :)