Hey nostr:npub1c0mpgcqpvffz4wmd0cmx8dzxtm9fukyz5yugx0n73fzzptlusnfqrns0qs nostr:npub1nje4ghpkjsxe5thcd4gdt3agl2usxyxv3xxyx39ul3xgytl5009q87l02j
Master Key is a new thing we introduced that allows you to have one seed to generate keys to Nostr, Liquid network, bitcoin onchain and LNURL login. It is not related to lightning wallet itself and does not back it up.
Sorry this is confusing. We are working on better onboarding users to Master Key. Here's a short guide about it: https://guides.getalby.com/alby-guides/alby-browser-extension/features/master-key
You still can use Nostr without Master Key